m - 

# LIBRARY OF CONGRESS, i 

| 



♦ 



f UNITED STATES OF AMERICA.! 



A TEXT-BOOK 



ON 



PHYSIOLOGY. 



FOR TLTE USE OF 



SCHOOLS in COLLEGES. 



BEING AN ABRIDGMENT OF THE AUTHOR'S LARGER WORK ON 
HUMAN PHYSIOLOGY. 

BY 

JOHN WILLIAM DRAPES, M.D., LL.D., 

AUTHOR OP 

A " TREATISE ON HUMAN PHYSIOLOGY," AND OF A u HISTORY OF 

THE INTELLECTUAL DEVELOP3LENT OF EUROPE," ETC. 



EllustrateU tottj) ncarlr 150 tt ! ootJ linflrabtngs. 



N E W T R K : 
HABPKB I BROTHERS, PUBLISHERS, 

I I a RIL11 I Q D I I J 

18- 






Entered, according to Act of Congress, in the year one thousand 
eight hundred and sixty-six, by 

HARPER & BROTHERS, 
i 

In the Clerk's Office of the District Court of the Southern District 
of New York. 



sX' 



/b 






PREFACE. 



A desire has been frequently expressed by pro- 
fessors and teachers who have used my large work 
on " Human Physiology," that I should publish an 
abstract of it, suitable for use as an elementary text- 
book in colleges and schools. 

I have accordingly in this work endeavored to sat- 
isfy that wish, and to furnish a book sufficiently sim- 
ple and compendious for such general use, and yet 
representing the state of the science at the present 
day. 

Among my original contributions to the science, 
many of them first printed in various periodicals, 
and introduced into the previous larger work and 
also in this, I may mention the Electrical Theory of 
Capillary Attraction, Explanation of the Selecting 
Action of Membranes, Cause of the Coagulation of 
the Blood, Theory of the Circulation of the Blood, 
Explanation of the Flow of Sap, Endosmosis through 
thin Films, Measure of the Force of Endosmosis, 
Respiration of Fishes, Action of the Organic Muscle 
Fibres of the Lungs, Allotropism of Living Systems, 
New Observations on the Action of the Skin, Func- 
tions of Nerve Vesicles and their Electrical Analo- 
gies, Function of the Sj 7 mpathetic Nerve, Explana- 
tion of certain Parts of the Auditory Apparatus, par- 
ticularly the Cochlea and Semicircular Canals, the 



IV PREFACE. 

Theory of Vision, the Theory of Muscular Contrac- 
tion. 

Of the wood-cuts, many are from photographs made 
by myself, particularly the microscopic photographs. 
The mode of producing these was first invented by 
me, and my " Human Physiology," published in 1856, 
was copiously illustrated with them. 

The original engravings in this volume are, Figs. 3, 
7, 8, 15, 16, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 
30, 31, 32, 33, 34, 35, 39, 40, 41, 42, 47, 48, 49, 51, 52, 
53, 54, 55, 56, 57, 58, 60, 67, 72, 73, 76, 79, 100, 103, 
104, 105, 108, 109, 114, 115, 119, 120, 121, 122, 123, 
124, 125, 126, 127. The rest are derived from stand- 
ard authors. A list of them, duly accredited to their 
proper sources, will be found page 1, etc., of the larger 
work. 

For the sake of facilitating the progress of the be-, 
ginner, questions have been appended to each page, 
as was done in my previous text-books on Chemistry 
and Natural Philosophy. Their utility has been gen- 
erally recognized by instructors. 

John William Draper. 

University, £?ew York, 1866. 



CONTENTS. 



CHAPTER PAGE 

I. Conditions of Life 1 

II. Of Food U 

III. HlSTOGENETIC DIGESTION 26 

IV. Calorifacient Digestion 52 

V. Absorption, Lacteal and Lymphatic 66 

VI. Absorption by the Blood-vessels 83 

VII. Of the Blood 91 

VIII. Circulation 108 

IX. Respiration 134 

X. Animal Heat 158 

XI. Secretion 175 

XII. Excretion 190 

XIII. Nervous System 210 

XIV. Nervous System — Continued 227 

XV. Hearing 261 

XVI. Vision 277 

XVII. Touch 295 

XVIII. Smell 299 

XIX. Taste 302 

XX. Animal Motion 305 

XXI. Voice 321 

XXII. Development 327 

XXIII. Reproduction 336 

XXIV. Growth 357 

XXV. Sleep and Death 363 



HUMAN PHYSIOLOGY. 



CHAPTER I. 



Conditions of Life. — Nature and Sources of Substances 
supplied to the Body. — Annual Quantities required. 
— Animals do not create^ but transform Substances. 
— Properties and Quantities of Matter received by the 
System. — Properties and Quantities of those it re- 
stores. — Heat of the Body arises from Combustion. 
— Cooling Agencies in an Animal. — Necessity of 
Repairs in the System. 

For the maintenance of the life of man three chem- 
ical conditions must be complied with. He must be 
furnished with air, water, and combustible matter. 

The supply of a part of these necessaries of life is ad- 
justed to the urgency of the want. The act of breath- 
ing is incapable of delay, but the air is accordingly ev- 
ery where present, and always fit for use. We can bear 
with thirst for a little time, and the earth here and there 
furnishes her springs and other stores of water. But 
far otherwise is it in the obtaining of food. It is the 
lot of all animals to secure nourishment by labor, and 
even of men the larger proportion, both in civilized and 
savage countries, submit to a hard destiny. To obtain 
their daily bread is the great object of life. 

What is the philosophical explanation of this neces- 
sity for a supply of air, of water, of food? Why is it 
that the system will bear so little delay? 

The answer to these questions is an answer of omi- 
nous import. The condition of life is death. No part 
of a living mechanism can act without wearing away, 
and for the continuance of its functions there is there- 
in! absolute necessity for repair. 

What arc the chemical conditions necessary for the support of 
life? What is the condition under which the living body acts ? 

A 



2 EQUILIBRIUM OF LIFE. 

Life, far from being a condition of immobility, is there- 
fore a condition of ceaseless change. An organism, no 
matter of what grade it may be, is only a temporary 
form, originating in myriads of particles passing through 
a determinate career. It is like the flame of a lamp, 
which presents for a long time the same appearance, 
being ceaselessly fed as it ceaselessly wastes away. 
But we never permit ourselves to be deceived by the 
simulated unchangeableness offered by such a natural 
object. We recognize it as only a form arising from 
the course the disappearing particles take. And so it 
is with man.' He is fed with more than a ton weight 
of material in a year, and in the same time wastes 
more than a ton away. 

To have a uniform standard of reference, we may as- 
sume one hundred and forty pounds as the weight of 
an adult healthy man. Now the constant consumption 
of food, water, and atmospheric air tends steadily to 
increase that weight, and in a very short time a dis- 
turbance arising from these sources would be percepti- 
ble, were there not some causes of compensation. But 
even after a year, if a state of health is maintained, the 
weight may remain precisely what it was, and this may 
continue year after year in succession. The consump- 
tion of large quantities of solid, liquid, and gaseous mat- 
ter does not therefore necessarily add to the weight. 

There are two periods of life for which this observa- 
tion does not hold good. They are infancy and old age. 
During the former the weight increases from day to day, 
and during the latter it slowly declines. 

If there be thus causes for the increase of weight of 
the living system, there are also causes for its diminu- 
tion. Setting aside minor ones, these may be chiefly 
enumerated as loss by excreted, by transpired and ex- 
pired matters. By transpired matters are meant such 
as escape under the form of liquids and gases from the 
skin ; by excreted, such as escape from the kidneys ; 
and by expired, vapors and gases escaping from the 

In what respect does the animal body represent a flame ? How 
much material does a man require in the course of a year? What 
is the standard weight of an adult man ? How is it that that stand- 
ard weight is maintained ? To what periods of life does that princi- 
ple not apply ? What are the chief causes of diminution of weight ? 



ANNUAL EECEirTS AND WASTE IN MAN. 3 

lungs. There is, therefore, a tendency to an increase 
and a tendency to a diminution of the weight, and, in 
the condition of equilibrium we are considering, these 
must balance one another. 

If a man of the standard weight abstains from the 
taking of water and food, a good balance will prove that 
in the course of less than an hour he has become light- 
er. If he still persists, it needs no instrument to detect 
what is going on ; the eye perceives it, for emaciation 
ensues. 

How, then, is it possible for a living being to continue 
at its standard, except the causes of increase are precise- 
ly equal to the causes of diminution ? We may there- 
fore assert that the sum total of food, water, and atmos- 
pheric air taken in a given period of time is precisely 
equal to the sum total of all the losses ; for, if the re- 
ceipts were greater, the weight must increase ; if the 
losses were greater, the weight must diminish. Persist- 
ency in this respect proves equality, and the case is just 
as simple as in the common affairs of life ; he who pays 
less than he receives grows rich ; if his payments are 
more than his receipts, he becomes poor ; but his con- 
dition is unchanged if his payments and receipts are 
equal. Infancy, old age, and manhood answer to these 
circumstances respectively. 

From the army and navy diet scales of France and 
England, which of course are based upon the recognized 
necessities of large numbers of men in active life, it is 
inferred that about 2^ pounds avoirdupois of dry food 
per day are required for each individual; of this about 
three quarters are vegetable and the rest animal. At 
the close of an entire year the amount is upward of 800 
pounds. Enumerating under the title of water all the 
various drinks — coffee, tea, alcohol, wine, etc. — its esti- 
mated quantity is about 1500 pounds per annum. That 
for oxygen may be taken at 800 pounds. 

With these figures before us, we are able to see how 
the case stands. The food, water, and air a man re- 
ceives amount in the aggregate to more than 3000 

Explain the manner in which the losses and receipts balance each 
othrT. What i-; the amount of dry food, of water, and of oxygen 
required annually ? What is the annual aggregate of the receipts ? 



4 ANNUAL RECEIPTS AND WASTE IN MAN. 

pounds a year ; that is, to about a ton and a half, or to 
more than twenty times his weight. 

The condition of equilibrium just set forth, moreover, 
leads to the conclusion that the aggregate weight of 
excreted, transpired, and expired matter is the same for 
the same period of time. In round "numbers, we may 
take it at a ton and a half. 

It can not be questioned that the materials rendered 
back to the external world, after having subserved the 
purpose of the animal and passed through its system, 
are compounds of those originally received as food, 
drink, and air, though they may have assumed in their 
course other, and perhaps, in our estimation, viler forms. 
Recognizing as indisputable the physical fact that not 
an atom can be created any more than it can be de- 
stroyed, we should expect to discover in the substances 
thus dismissed from the system every particle that had 
been taken in. 

What, then, is man ? Is he not a form, like the flame 
of a lamp or a waterfall, the temporary result and rep- 
resentative of myriads of particles that are fast passing 
through states of change — a mechanism, the parts of 
which are unceasingly taken asunder and as unceasing- 
ly replaced ?* The appearance of corporeal identity he 
presents year after year is only an illusion. He begins 
to die the moment he begins to breathe. One particle 
after another is removed away, interstitial death occur- 
ring even in the inmost recesses of the body. 

From these general considerations we infer that the 
essential condition of life is waste of the body ; and this 
not only of the body in the aggregate, but even of each 
of its particular parts. Whatever part it may be that is 
exercised is wearing away, and wherever there is activ- 
ity there is death. And since parts that are dead are 
useless, or even injurious to the economy, the necessities 
simultaneously arise, first, for their removal, and, second, 
for repair. Much of the complicated mechanism of ani- 
mal structures is for the accomplishment of this double 
duty. 

What is the annual aggregate of the losses ? Under what circum- 
stances does interstitial death take place ? What is the general use 
of the mechanism of animal structures ? 



NATURE OF MATTERS RECEIVED. 5 

Physiological Standard Table. 

Diurnal Ingesta of a Man whose weight is 140 lbs. avoirdupois. 

Weight of bodv H0.000 

Water 4.109 

Oxygon 2.192 

Dry vegetable food 1.687 

Dry animal food 563 

It is to be received as an axiom admitting no contro- 
versy, that organic systems, whether vegetable or ani- 
mal, whether humble or elaborately developed, possess 
no power of creating material. Their function is of ne- 
cessity limited to the mere transformation of substances 
furnished to them. From this it follows, even in the 
case of man, that the substances dismissed from the sys- 
tem are metamorphosed forms of those which have been 
received, and that, whatever their appearance may be, 
they must have arisen from the reaction of the food, 
water, and air upon one another. 

This reaction we may proceed to view as a purely 
chemical result ; for, casting aside all the hypotheses of 
the older physiology, and permitting ourselves to be 
guided by the harmonies of nature, we should expect to 
recognize in the changes taking place in organic sys- 
tems, and in the phenomena attending those changes, 
the same results which arise in the artificial or experi- 
mental reaction of food, water, and air on each other. 
A very superficial examination of the facts shows at 
once the correctness of this expectation. On such a 
preliminary examination we now enter, premising it 
with some general remarks needful for our purpose on 
the nature and properties of food, water, and air. 

1st. Of Food. — Xo article is suitable for food except 
it be of a combustible nature. Its chemical constitution 
must be such that if its temperature be raised to a prop- 
i ee with a due access of atmospheric air it will 
take tire and burn, and the products of its combustion 
must be carbonic acid gas and water, or those sub- 
stances with nitrogen or its compounds. 

2d. Of Water. — This may be taken as the type and 

S an animal create or only transform the Bubstaiices it re- 
ceives ? How have the rabstancea dismissed from the system origin- 
ated ? What are the chemical properties of food ? 



6 NATURE OF MATTERS RESTORED. 

representative of all the various liquids used as drinks. 
It evaporates at any temperature, even at those lower 
than its freezing point, and in this evaporation produces 
cold. Water vaporizing from the skin absorbs 1114 de- 
grees of heat, and hence exerts a most powerful refrig- 
erating action. Over saline substances there are few 
bodies which exercise so general a solvent effect. In 
virtue of this property, it is enabled to introduce in the 
dissolved state such compounds as are wanted for the 
nutrition of the system, and in the same manner to car- 
ry away the wasted products of decay. 

3d. Of Atmospheric Air. — The active principle of the 
air is oxygen gas, the effects of which are moderated by 
the presence of a large quantity of nitrogen — four-fifths 
of the air consisting of this latter substance. Physio- 
logically, we often use the terms atmospheric air and 
oxygen synonymously. 

The chief materials a living being receives from the 
external world are, therefore, combustible matter, wa- 
ter, oxygen gas ; and out of the action of these upon 
one another all the physical phenomena of its life arise. 

Such being the nature and properties of the things re- 
ceived, we may next examine in the same general man- 
ner those dismissed from the system. Here, at the very 
outset, we encounter the important fact that they are 
oxidized or burned bodies. 

1st. As respects the excretions. Their liquid part, 
water, is an oxide of hydrogen, of which, though the 
greater portion may not have been produced in the 
economy, yet a certain quantity unquestionably has. In 
them, too, may be found sulphuric acid, an oxide of sul- 
phur ; phosphoric acid, an oxide of phosphorus ; and 
urea, the representative of bodies arising when process- 
es of oxidation have been going on. 

2d. The expired and transpired matters present simi- 
lar burned compounds. At the head of these products 
stand carbonic acid gas, an oxide of carbon ; and water, 
which, as we have already said, is an oxide of hydrogen. 

What are the chemical properties of water ? and of atmospheric 
air ? What are the properties of the substances dismissed from the 
system ? What are water, sulphuric, and phosphoric acids ? Un- 
der what circumstances does urea arise ? What are the chemical 
qualities of the expired and transpired matters? 



NATURE OF MATTERS RESTORED. 7 

"We here omit any consideration of the nature or consti- 
tution of the fsecal matter, because much of it has never 
been properly in the interior of the system, though it 
lias passed through the intestine. 

The general result we arrive at is then, that the food 
consists of combustible matter, and that the substances 
dismissed from the economy are oxidized bodies. A 
burning must, therefore, have been going on, and this 
could only have been accomplished by the air intro- 
duced by breathing acting upon the substance of the 
body itself and its contents, and, to repair the waste 
which must have ensued, a due weight of food has been 
required. Since this, in its turn, as a part of the living 
mechanism, is destined to undergo the like destructive 
action, we may present the entire series of facts under 
consideration correctly by regarding them as arising re- 
motely from the action of the air upon the food. 

With this statement before us, we next inquire what 
ensues when substances appropriate for food are ex- 
posed in artificial experiments at a certain temperature 
to the action of atmospheric air. 

.V piece of flesh, or of any vegetable body, consist- 
ing of carbon, hydrogen, oxygen, and nitrogen, submit- 
ted to those conditions, undergoes combustion. Its car- 
bon, by uniting with oxygen, produces carbonic acid, 
its hydrogen for the most part water, but a residue 
thereof, combining with the nitrogen, may give rise to 
the production of ammonia. If there be any sulphur 
and phosphorus present, they also burn, and salts of sul- 
phuric and phosphoric acids are the result. 

Such is what occurs outside of the body in a common 
case of artificial combustion where atmospheric air has 
access. The constituents of the food thus satisfy their 
chemical affinities, and the compounds we have men- 
ded arise. Now it is a fact of the utmost significance 
that the compounds thus originating from the direct ar- 
tificial burning of matters proper for food are the very 
same that are dismissed from the animal system in 
which food has been submitted to the air introduced by 

How do we know thai combustion must tnko place in the body? 
What is the result of the artificial combustion of food? What are 

the product- arising in the natural and artificial combnstion of food? 



8 PRODUCTION OF HEAT. 

respiration. They are such substances as carbonic acid, 
water, ammonia, sulphates and phosphates. 

The facts thus set forth warrant the following state- 
ments. The matters a man receives as food are com- 
bustible bodies ; those dismissed from his system have 
been burned. To that, as to' any other such burning, 
oxygen gas is absolutely requisite. There is, therefore, 
a plain conclusion before us, which, in its far-reaching 
consequences, covers the whole science of physiology, 
and betrays to us the function discharged by every ani- 
mal, viz., that oxidation is incessantly going on in the 
interior of the system through the agency of atmospher- 
ic air introduced by the process of breathing. 

An animal, from this point of view, is an oxidizing ma- 
chine, into the interior of which atmospheric air is con- 
stantly introduced. The active constituent, oxygen, sat- 
isfies its chemical affinities at the expense of those parts 
of the system that are wasting away. And as the act 
of breathing, that is, the introduction of this gas, takes 
place day and night, waking and sleeping, so too must 
the production and removal of burned bodies. To com- 
pensate for the loss, nearly 1000 pounds weight of com- 
bustible matter must be used in the course of a year, 
and, for reasons to be examined in detail presently, three 
quarters of a ton of water. 

But carbon by uniting with oxygen can not turn into 
carbonic acid, nor can hydrogen turn into water, nor ni- 
trogen into ammonia, without heat being produced. 
The very meaning we attach to the term indicates that 
every process of burning is attended with the liberation 
of heat. 

In domestic economy, we protect ourselves from the 
cold weather of winter, or attain any high temperature 
we want by the oxidation of some of the forms of car- 
bon, such as wood or coal, in fire-places or stoves. We 
know that for the production of a given quantity of 
heat a given weight of combustible matter and of air is 
required, and that by employing various mechanical con- 
trivances for increasing the draught we can accelerate 
the burning. 

How is it that animal heat is produced ? What is the effect of 
oxygen in the interior of the body ? Is there any relation between 
the amount of heat set free and the amount of oxygen consumed? 



REGULATION OF HEAT. 9 

Man, in a state of health, maintains a nearly uniform 
temperature. Neglecting slight variations, to be here- 
after critically examined, it is 98 degrees. For the most 
part, it is immaterial in what climate of the earth he 
may reside, whether in the cold polar regions or the 
torrid zone, he is so constituted that, either through the 
provisions of his own organization, or by resorting to 
the adventitious aid of clothing, or to special articles of 
food, he can maintain himself at about the same degree; 
and as all this heat arises from interstitial oxidation con- 
tinually taking place, it is obvious that within certain 
limits he has control over it. Thus, in the winter he 
sometimes resorts to violent muscular action in order to 
increase the rapidity of respiration and the destruction 
of muscular tissue ; for the greater the quantity of air 
introduced in a given period of time, the higher the 
temperature rises, just as when we close the door of a 
stove, or place a blower on an anthracite fire, an in- 
creased draught is occasioned and the quantity of heat 
is increased. To breathe with rapidity and depth is 
certain to raise the temperature. 

On the contrary, in summer, when the heat is oppress- 
ive, we instinctively abstain from muscular exertion, 
tranquil and slow respiration goes on, and the tempera- 
ture is kept down. Again, there are means of occasion- 
ing an increased liberation of heat by changing the na- 
ture of the food and using highly combustible material, 
such as the various kinds of alcoholic preparations. 
The chemical constitution of alcohol is such that in the 
act of burning, carbonic acid and water are produced 
with the liberation of so much heat that chemists find it 
one of the most suitable means of attaining a high tem- 
perature. On taking preparations of tins substance, 
such as distilled liquors or wines, the first effect is the 
production of a gefiial warmth all over the body, intoxi- 
cation eventually coming on as a secondary result. 

These remarks arc not limited in their application to 

our own specie the whole animal world furnishes us 

with commentaries on their troth. Man maintaining a 

What i- the temperature of man? Does it vary in different cli- 

mates ? In what manner may that temperature be incidentally 

\ In what manner may it he reduced? What ifl the (fleet 

un the temperature when distilled liquors or vrinefl are used? 

A 2 



10 USES OF WATER. 

temperature, as has been said, of about 98 degrees, oth- 
er animals are at other degrees, some being cold-blood- 
ed and some hot. The particular point they reach de- 
pends, as direct observation shows, on the quantity of 
oxygen they consume, or, in other words, on their res- 
piration. Birds, whose breathing mechanism is by far 
the most elaborate and extensively developed, have by 
far the highest temperature. The snake or the tortoise, 
whose rate of respiration is very slow, consume but lit- 
tle oxygen, and have a correspondingly low degree of 
heat. And in those creatures which at one period of the 
year are in full activity, but at another lie dormant or 
hibernate, as they begin to respire more slowly their 
temperature begins to decline, and when they have sunk 
into their winter's sleep their breathing is scarcely per- 
ceptible, and their warmth scarcely above that of the 
surrounding air. 

In what has been thus far said we have been consid- 
ering those operations of the system that tend to the 
production of heat, and the maintenance of the whole 
mass of the body at a temperature above that of the 
surrounding air. But it is obvious that provision must 
be made to prevent any undue rise, so that between 
those causes of elevation and these of depression a due 
equilibrium may be maintained. If a very large quan- 
tity of combustible matter, under the form of food, and 
about an equal weight of oxygen, are necessary for ob- 
taining a proper heat, we should also recollect that near- 
ly three quarters of a ton of water are consumed each 
year. The duty this water discharges we may next con- 
sider. 

That duty is twofold: 1st. The removal of solid ma- 
terial in a state of solution ; and, 2d. The production 
of cold by evaporation. The cooling agency is of most 
interest to us in our present inquiry, but a few remarks 
as regards the removal of solid matter may not here be 
misplaced. 

1st. Water, then, exerts its solvent power for the re- 

What is the connection between respiration and animal heat? 
How is it in the case of birds, snakes, and tortoises ? How is it in 
the case of hibernating animals ? What are the causes of the cool- 
ing of the body ? Describe the double duties of water in the sys- 
tem. 



HOW REMOVED FROM THE SYSTEM. 11 

moval of all those substances which, arising incessantly 
in the animal system, can not assume either the vapor- 
ous or gaseous state. In this condition are the differ- 
ent saline bodies, such as the sulphates coming from the 
destruction of the muscular tissues, as voluntary and in- 
voluntary motions are performed; or the phosphates 
produced by the destruction of cerebral and nervous 
matter. In the same condition stand nearly all the ni- 
trogenized results of the destruction of the soft parts, 
and which are to a great extent to be removed as urea. 
Water dissolving with more or less facility these vari- 
ous bodies permits their escape from the system by the 
secreting action of the kidneys. 

The skin is no inefficient auxiliary to the kidneys in 
effecting this removal of water charged with soluble 
matters. All over its surface are scattered in profusion 
the ducts of the perspiratory glands, consisting of a con- 
voluted tubing abundantly supplied with blood-vessels. 
The final mode of action of these glands depends on ex- 
traneous circumstances. Most commonly the fluid is 
carried away under the form of a vapor or insensible 
perspiration, but when the secretion goes on more rap- 
idly, or the dew-point of the surrounding air is high, it 
then accumulates as drops of sweat. The amount of 
water thus removed, even by insensible perspiration, is 
greater than might be supposed, yet it corresponds with 
the extent of the provision. The length of the water- 
secreting tubing in the skin of a man is about twenty- 
eight miles. 

Thus by the action of the kidneys and the skin large 
quantities of water are dismissed, either under the liquid 
or vaporous form. A third organ is concerned in this 
important duty. It is the lungs. These, however, are 
limited in their operation to its exhalation as vapor or 
steam. That water abundantly escapes from them is 
plainly shown when the days are cold, the moisture as it 
from the respiratory passages condensing into a 

ible cloud when it encounters the air. It is estimated 
that the loss of water by the skin and lungs conjointly 

What a<k. rent power? Under what form 

remoTed from theiystem? What u the Length of water-tubing 

in the -kin? To - of snbstancefl i> the action of the Innga 

limited ? How may it be proved that water is removed by the lungs? 



12 COOLING BY EVAPORATION. 

is about 18 grains in a minute, of which 11 pass off 
from the skin and 7 from the lungs. 

2d. Water also exerts a cooling influence, arising from 
its evaporation from the surface of the skin and the cells 
of the lungs. The difference between water in the state 
of an invisible vapor and in the liquid condition consists 
in this, that the vapor contains 1114 degrees of heat 
which the liquid does not. When, therefore, it evapo- 
rates from a surface of any kind, as from the skin, it ob- 
tains therefrom that large amount of latent heat, and so 
tends to cause the temperature to decline. Not that 
this is the only cooling agency at work. Radiation 
might also be mentioned ; for, just as a warm, inorganic 
body cools by the escape of radiant heat from it, so too 
does a living being. 

These considerations explain how an equilibrium of 
temperature is established. By the process of respira- 
tion there is a constant tendency to increase the heat ; 
but by evaporation of water, radiation, and other cool- 
ing causes, there is a constant tendency to diminish it. 
A balance is struck between the two processes, and in 
man a temperature of 98 degrees is kept up. 

This average temperature is, however, easily departed 
from. Through some trivial cause the cooling agencies 
may be interfered with, and then, the heating processes 
getting the superiority, a high temperature or fever 
comes on. Or the reverse may ensue. In Asiatic chol- 
era, the constitution of the blood is so changed that its 
discs can no longer carry oxygen into the system, the 
heat-making processes are put a stop to, and, the tem- 
perature declining, the body becomes of a marble cold- 
ness characteristic of that terrible disease. 

The animal mechanism is thus the focus of intense 
chemical changes, and great quantities of material are 
required in very brief spaces of time for its support. 
We have seen what is the use of the combustible mat- 
ter employed as food, what of the water, what of the 
air, how, these reacting on one another, a high but reg- 
ulated temperature is kept up. 

On what does the cooling effect of water depend? How is the 
equilibrium of heat maintained ? Under what circumstances is the 
standard temperature departed from ? 



PHYSICAL MECHANISM OF MAX. 13 

Much of what has been thus far said has had reference 
only to the destruction of tissues. This waste of matter 
arises partly to give origin to the heat required by ani- 
mals, and partly as a consequence of intellectual activi- 
ty and muscular motion ; for no movement can be made 
without a destruction of muscular fibre, and all mental 
and nervous actions imply the waste of a certain quan- 
tity of vesicular substance. 

But of course such a destruction of tissue must be 
compensated by repair if a normal condition and health 
arc preserved. The action of the air is not directly 
upon the food, for intermediately and temporarily the 
food is converted into the living mechanism. The dead 
material is awakened into life, and for a time, though 
only for a time, becomes a portion of the living and feel- 
ing mass. 

The functions and actions we have been considering 
imply the provision of many complicated mechanisms. 
There must be means for effecting the introduction of 
the air ; these, in man, depend on calling into operation 
its pressure. A system of tubes is necessary for its dis- 
tribution to the points at which it is required, and in 
like manner a system is required for carrying away the 
wasted products of decay. The new material destined 
to replace the parts which are thus disappearing, and to 
keep the economy in repair, must be submitted to such 
processes of mechanical and chemical preparation that 
it may be dissolved in the blood, and carried wherever 
it is wanted. It must therefore be cut and crushed by 
teeth driven by powerful muscles, dissolved by acid and 
alkaline juices in digestive cavities set apart for that 
purpose. From these it must be taken by arrangements 
that can absorb it and carry it into the torrent of the 
circulation. Physical means must be resorted to, not 
only for the impulsion of these newly-absorbed nutritive 
juices, but likewise to drive the blood in its proper ca- 
■r of circulation. It is needless here to explain how 
tli" most refined principles of hydraulics arc brought into 
play, or how forces of compression and elasticity arc 

HOW is it that the f I much matter Blues? What mech- 

anisms are requisite for the femora] of waste and for repair? What 

operations must the food l>e submitted to before it can be introduced 
into the system ? 



14 SUBDIVISIONS OF PHYSIOLOGY. 

introduced ; how that there are valves which open only 
in one way to let the current pass, or how some of these, 
as in the like human contrivances, are tied down in their 
action by cords. Moreover, since it is required that the 
animal shall go in search of its food, muscles of locomo- 
tion, acting upon purely mechanical principles on the 
bony skeleton, must be resorted to, and so the animal 
structure becomes a most elaborate and complicated 
machine. 



CHAPTER II. 

OF FOOD. 

The natural Subdivisions of Physiology. — Of Food: 
its Sources and Classification — its Value not alto- 
gether dependent on its Composition. — Of Milk : its 
Composition, and Use of its Water, Casein, Sugar, 
Sutter, and Salts. — Variations in the Composition 
of Milk. — Of Bread. — Of mixed Diets. — Nutrition 
of carnivorous and herbivorous Animals. — Food 
formed by Plants and destroyed by Animals. — Uses 
of mixed Food and Cooking. 

Physiology possesses a very great advantage over 
many other sciences in offering its leading problems and 
doctrines in a certain well-marked order or sequence, a 
connected whole, with only here and there points of di- 
gression, but those points often of very striking interest. 
Thus pursuing the train of reflections entered on in the 
preceding chapter, we should have to consider the na- 
ture of the food, the manner of its preparation by the 
process of digestion, the mechanism for taking it up 
from the cavities in which it has been so prepared, and 
that for distributing to every part. We should have to 
show the mode of its incorporation as a portion of the 
living mass, its duration in that condition, and the man- 
ner of its decay. We should have to describe by what 
physical means and through what mechanism the air is 
introduced to effect the destruction of the dying parts, 

What are the natural subdivisions of physiology ? 



SUPPLY OF FOOD TO ANIMALS. 15 

and how, as the consequence of this, a fixed tempera- 
ture is maintained. The causes occasioning variations 
of this temperature, and the manner in which the wasted 
products are removed by the skin, the lungs, the kid- 
neys, might next obtain our attention. The complica- 
ted machinery necessary to accomplish all these pur- 
poses requires to be made to act in unison in all its dif- 
ferent parts, a condition introducing to us the nervous 
system. A consideration of the structure and gradual 
development of that system leads to the structure of the 
various organs of sense, and to the operations of the in- 
tellectual principle itself. Thus in succession we should 
have to treat of digestion, absorption, circulation, respi- 
ration, secretion, nutrition, and innervation, and to close 
the whole with the consideration of reproduction. This 
is the order I propose to follow, and shall devote this 
chapter to the nature and qualities of the food. 

The supply of food to animals requires a more com- 
plicated provision than it does to plants, in which the 
elaborating organs, the leaves, presenting themselves 
superficially, are always in contact with the air, from 
which much of their nutriment is derived. And as one 
portion after another becomes exhausted, it is renewed 
by simple mechanical agencies, such as the trembling of 
the leaf, the warmth of the sun, or the winds. 

Food comes spontaneously to plants, they therefore 
need no powers of locomotion. But an animal must 
seek its food, and for this purpose is endowed with lo- 
comotion, involving the destruction of tissue. In a 
chemical point of view, plants are organizing, animals 
destroying machines. 

To obtain for animals the necessary supply of nutri- 
ment, the resources of nature are displayed in the most 
wonderful contrivances. According as their modes of 
life may be, one takes its food with its teeth, another 
with its lips, another with its fore member, another 
winds around it its whole body. The geometrical spi- 
der weaves a net, and lies in wait for his prey; the ant 
lion digs a pit in the sand. Some rely upon labor, some 
upon force, some upon fraud. Man depends upon all. 

What are the sources of food for plants? In what manner is it 
brought to them ? In the case of animals, how is the supply of food 
taken? 



16 HISTOGENETIC AND CALOEIFACIENT FOOD. 

Viewed as regards its physiological distinction, the 
food is conveniently considered as of two kinds : His- 
togenetic or tissue-making, and Calorifacient or heat- 
making. Histogenetic food, of which albumen, casein, 
fibrin, are examples, furnishes the chemical substances 
— carbon, hydrogen, oxygen, nitrogen, sulphur, chlorine, 
phosphorus, iron, potash, soda, lime, etc. Calorifacient 
food, of which starch, sugar, oil, fat, are examples, fur- 
nishes carbon and hydrogen mainly. In consequence 
of this chemical constitution, tissue-making food is some- 
times called nitrogenized, and heat-making non-nitro- 
genized food. The former is also sometimes designated 
nutritive, and the latter respiratory. 

It is, however, to be distinctly understood that these 
divisions are only adopted for the sake of convenience, 
and that they have no natural foundation. Thus it will 
be found, when we examine the functions discharged by 
the fats, that though they are non-nitrogenized bodies, 
and are, therefore, considered as belonging to the class 
of respiratory food, there is every reason to believe that 
they are essentially necessary to tissue development, 
and that the metamorphoses of nitrogenized bodies can 
only go on in their presence. They are, therefore, as 
truly essential to nutrition as are the latter substances. 

So, too, as respects the albuminoid bodies. They are 
not limited to nutrition. In their decay or descending 
metamorphosis in the organism, they give rise to the 
evolution of heat, and are at last dismissed as products 
of oxidation. They are, therefore, as far as this goes, as 
much respiratory food as are the fats themselves. 

It has been supposed that the tissue-making power 
of any kind of food depends on the quantity of nitrogen 
it contains, and that its value may therefore be determ- 
ined by chemical analysis. Upon this principle tables 
have been constructed, showing the agricultural worth 
of different articles of forage for domestic animals. 
But, as will be found hereafter, these tables are not of 

How many physiological kinds of food are there? What is histo- 
genetic food ? What is calorifacient food ? What are tissue-mak- 
ing, heat-making, nitrogenized, and non-nitrogenized food respect- 
ively? Are albuminoid bodies exclusively nutritive? Do they ever 
give rise to the evolution of heat ? Are they ever respiratory ? Does 
the value of food depend on its composition ? 



composition of milk. 17 

the use supposed. Without entering into details at 
present, the case of gelatin may be taken as an example ; 
this, though a substance abounding in nitrogen, possess- 
es no tissue-making value, but in reality belongs to the 
calorilacient class, and therefore its administration in 
the sick-room, under the various well-known forms of 
jellies, soups, etc., is altogether deceptive as regards 
any nutritive power, since it undergoes speedy oxida- 
tion in the system. 

The same remark applies to tables showing the amount 
of caloric furnished by different varieties of heat-making 
food. The quantity of heat set free during the combus- 
tion of a substance depends not only on the nature of 
the elements composing it, but also on the particular 
states in which they occur. Combustibles may have 
the same chemical composition, but very different heat- 
ing power. 

Food, typically perfect, is presented by nature to the 
young of various animals. In milk, or in the egg, there 
must be whatever is necessary for the growth of the 
tissues, and for the performance of the functions. An 
examination of milk will therefore illustrate the essential 
characters of the different elements of food. 

Composition of Milk. 

Water 873. 

Casein . 48. N 

Sugar of milk 44. 

Butter 30. 

Phosphate of lime 2.3 

Other salts 2.7 

1000.0 
In this we notice, first, the large proportion of water 
present, almost nine tenths of the whole amount. The 
double duty of this water has already been mentioned, 
first, to remove from the system effete substances, sec- 
ond, to regulate the temperature by evaporation. We 
might have added that it also imparts a due fluidity to 
the blood. These are conditions as necessary to the in- 
fant as to the adult, and it should be remembered that 
two thirds of the weight of the body are water. 

What is remarkable in the rase of gelatin? On what (loos the 
amount of heat furnished by the combustion of food-articles depend? 
What is the composition of milk? State the relative quantity of 
water it contains. What i> the use of the water? 



18 CASEIN AND ALBUMEN. 

Next follows the nitrogenized principle casein, closely 
related in composition to muscular flesh. It is the tis- 
sue-making, histogenetic, or nutritive element of the 
milk, and has been elaborated from the albuminoid sub- 
stances of the mother's system. It is to be converted 
into the muscular and other soft tissues of the infant. 

Casein is one of a group designated as the neutral ni- 
trogenized bodies. Albumen, fibrin, and globulin belong 
to it. From an opinion that these all contain the same 
organic radical, they are often termed the protein bod- 
ies, a designation retained rather from its convenience 
than correctness. They appear to exist in two different 
physical conditions, soluble and insoluble in water ; they 
all contain sulphur, and exhibit a proneness to pass into 
the putrefactive fermentation. As this takes place when 
they have reached a certain stage of decay, they act 
upon other bodies as ferments. Their constitution is 
said to be represented in common by the formula 

C 48 H 36 O u N 6 . 
Of the whole group, albumen may be taken as the type 
and most important member. Indeed, as will be found 
hereafter, in the process of digestion the others are in- 
variably converted into modifications of it. The white 
of the egg and the serum of the blood are usually refer- 
red to as examples of albumen, though they differ in 
several particulars from one another. Albumen forms 
basic, neutral, and acid compounds. A basic albuminate 
of soda is found in the egg and in serum of blood. 

Casein presents nearly the same constitution as albu- 
men, but differs from it in its physical properties ; for, 
while a solution of albumen is coagulable by heat, one 
of casein is not, but lactic and acetic acids coagulate it, 
though they have no such effect on albumen. While, 
so far as their protein nucleus is concerned, the two 
substances may be considered as agreeing in composi- 
tion, they differ in this respect, that casein appears to 
contain a less proportion of sulphur and no phosphorus. 
It is interesting to remark that, during incubation, ca- 
sein arises from albumen in the eggs of birds. 

To what class of substances does casein belong? How much is 
there of it in milk ? What is the imputed constitution of the protein 
bodies? Describe the properties of casein and albumen. What are 
the physical properties of casein ? 



COMPOSITION OF MILK. 19 

Closely allied to albumen and casein, and having the 
same imputed protein nucleus, is fibrin. It likewise ex- 
ists in two states, soluble and insoluble. Its solidifica- 
tion or coagulation can be produced by the action of 
sulphuric ether, which does not affect albumen. More- 
over, in the coagulated state fibrin decomposes the deu- 
toxide of hydrogen, but albumen does not. The most 
important difference between them is, that in the act of 
coagulation albumen shows no disposition to assume a 
definite structure, but fibrin does — fibrillating, as it is 
termed. The analogy of constitution and closeness of 
relation of the two substances is demonstrated by the 
fact that by nitrate of potash coagulated fibrin may be 
changed into albumen, and the same conversion is ac- 
complished in the stomach by the digestive juices. 

It has been affirmed, however, that fibrin contains a 
larger proportion of oxygen than albumen. This is sus- 
tained by physiological considerations respecting its or- 
igin. 

These remarks on the composition and physical prop- 
erties of casein, albumen, and fibrin, have been intro- 
duced for the purpose of illustrating the facility with 
which these bodies are mutually convertible, and more 
particularly for showing that there is nothing whatever 
mysterious in the casein or curd of milk, arising from 
the albuminous serum of the mother's blood, and being 
transmuted into the fibrin structure of the muscular 
;es of the infant. 

Returning now to our examination of the composition 
of milk, as set forth in the preceding table, we find that 
two respiratory elements are next upon the list: 1st. 
Sugar of milk. This is to be converted into lactic acid, 
partly by the agency of the saliva, and finally in intes- 
tinal digestion; 2d. Butter. This is the oleaginous or 
fatty portion ; a part of it is to be deposited in the adi- 
- for a time of need, and a part, along with 
the lactic acid and excess of sugar, is to be burned at 
once for the production of heat. 

The saline substance, phosphate of lime, is necessary 

In what r doee fibrin cxi>t ? What is meant by fibril- 

lating? Under what circumstance! may fibrin change into albu- 
men? Which probably contains the greater quantity of oxygen? 
What is the use of the sugar of milk ? and of the butter ? 



20 MILK AS FOOD. 

for the earthy portion of the skeleton, and probably the 
reason of the introduction of casein, to the exclusion of 
other protein compounds, depends on the power it pos- 
sesses of holding phosphate of lime in solution, not less 
than 6 per cent, of its weight of this earthy body being 
often obtainable from it. Among the other salts of the 
milk, chloride of sodium may be pointed out as of spe- 
cial importance. It undergoes decomposition in the 
system of the infant, its hydrochloric acid giving acidity 
to the gastric juice, its soda entering into the composi- 
tion of the bile and various salivary secretions. It also 
imparts solubility to albumen, and, in some degree, reg- 
ulates the facility with which that substance coagulates. 
It impedes the coagulation of fibrin. 

An infant finds in its mother's milk whatever it re- 
quires for the growth of its own body. In its system 
the curd resumes the form of albumen, or passes into 
the condition of fibrin, and in this manner its muscular 
tissues are made. The butter is deposited in the adi- 
pose cells, or burned at once for the production of ani- 
mal heat, a part of it, however, being incidentally con- 
sumed, as will be hereafter explained, in the fabrication 
of fibrin and for other histogenetic purposes. The phos- 
phate of lime is carried to the osseous system, now in a 
state of rapid increase, and bone is formed from it. 

But, though milk is so well adapted to the wants of 
infantile life, it is unsuited to the adult. Its nitrogen- 
ized principle, casein, though in sufficient quantity for 
the repair of muscular waste and development at the 
former period, is inadequate to these purposes at the lat- 
ter, when destruction, arising from the incessant activ- 
ity of the muscular system, is so greatly increased. It 
is interesting to remark how the composition of milk is 
modified when there is a necessity to meet these indi- 
cations, its nitrogenized principle being increased in the 
case of animals such as the cow and horse, the young 
of which commence locomotion almost at birth, or at an 
earlier period than the human infant. This excess of 
casein is necessary for the repair "of the resulting waste. 

What effect does casein exert over the solubility of phosphate of 
lime ? From what source is hydrochloric acid derived ? Why is 
milk the most perfect type of food? What duties do its various 
parts discharge in the infant body ? 



VARIOUS KIXDS OF MILK. — OF BREAD. 



21 



The Constitution of Milk. 



Source. 


Casein. 


Sugar. 


Butter. 


Goat's milk 


80 
63 
32 


40 

28 
36 


40 
40 

29 


Cow's milk 


Human milk 





This table presents an explanation of the un suitable- 
ness sometimes remarked in the milk of the cow when 
used for the nourishment of children. Milk which is 
adapted to the wants of the calf is not adapted to the 
functional wants of the child. Experience has taught 
the nurse that these difficulties may in part be removed 
by diluting it with water and sweetening it with sugar, 
the effect of this being to reduce the percentage of the 
nitrogenized element, the casein, and to increase that of 
the respiratory, and so approximate the composition 
more closely to that of human milk. 

Moreover, milk is not suitable as the sole nourish- 
ment of adult life, since it does not contain in sufficient 
quantity those phosphorized compounds necessary for 
the repair of the waste of the cerebral and nervous tis- 
sues, which at this period are much more active than in 
infancy. 

From this consideration of the nature and properties 
of the food of infancy, we may pass to the examination 
of that of the mature period. 

Experience has shown that, of all articles of food, 
bread made from wheaten flour meets best the require- 
ments of the adult life of man. It seems to contain all 
that is necessary for support. A very simple analysis 
will show that it presents both the respiratory and nu- 
tritive elements. 

If such flour be made into a paste with water, and be 
gradually washed with a larger quantity, an elastic co- 
herent mass is left, and the water assumes a milky tur- 
bidity. After a time it becomes clear, through the set- 
tling of a white precipitate. This is starch, a member 
of the respiratory group. The elastic substance is glu- 

In what resped dors the milk of different animals differ? How 

may the milk of the row be adapted to the use of the infant? Why 
i- milk UDSoited to adult life? From what Bubstance is the most nu- 
tritious bread made? Hqw may Hour be separated into its constitu- 
ent parts? To which class of elements does its stareh belong? 



22 OF MIXED DIETS. 

ten ; it is a true vegetable fibrin, mixed with another 
.nitrogenized body, gliadine. 

Thus, simply by washing in water, flour may be sep- 
arated into two physiological elements, respiratory and 
nutritive, the former being the starch, and the latter the 
gluten. The relative quantity of these substances dif- 
fers in different samples of flour, and, other things being 
equal, the greater the amount of gluten the more valua- 
ble the sample, because the more nutritious. 

But civilized man has greatly improved on the simple 
diet furnished by Nature, and, without knowing the im- 
mediate or philosophical reason, has added articles to 
increase the respiratory element. The proverb says, 
" It is good to have bread, but it is better to have bread 
and butter." Let us examine why it is so. 

Wheaten flour, in its relations to the animal system, 
is defective in one point — its respiratory element, the 
starch. Now the constitution of starch is, that in its 
dry state it contains much more than half its weight of 
water, none of its hydrogen being free, but all oxidized. 
It is, therefore, only by the use of very considerable 
quantities of bread that the necessary amount of respi- 
ratory food can be had for keeping up the temperature 
to the proper degree. But if butter be put upon the 
bread, the effect is different. In common with all ole- 
aginous bodies, butter contains an excess of hydrogen, 
and therefore, under the same weight, possesses a very 
high heating power. The defect of the flour is thus 
compensated, and by the use of quite a moderate quan- 
tity a high temperature can be maintained. 

From an examination of the diet-scales of the educa- 
tional and invalid establishments of London, the prisons 
and the hospitals, the result has been obtained that the 
nitrogenized should be to the non-nitrogenized food in 
weight as one to five. 

At a mature period of life, animals may be divided 
into two groups, first, the carnivorous, and, second, the 
herbivorous, or those that feed exclusively on flesh, and 

To which class of elements does its gluten belong? In what re- 
spect is wheaten flour imperfect ? Of what is starch to a large ex- 
tent composed? What is the effect of the use of butter? What 
should be the ratio of nitrogenized to non-nitrogenized food ? Into 
what groups may animals be divided ? 



FOOD OF CARNIYORA AND HERBIVORA. 23! 

those that feed on vegetable substances. Between these 
may, perhaps, be introduced a minor group, partaking 
of the manner of life of both. 

The carnivorous animal finds in its prey all that is re- 
quired for nutrition, and the discharge of its functions. 
Digestion under these circumstances is reduced to its 
simplest conditions, and is scarcely more than a process 
of solution. The digestive apparatus has but little com- 
plexity. The stomach may be regarded as a mere en- 
largement or pouch upon the alimentary canal, having, 
along with the intestine, the office of bringing the food 
into such a condition that it can pass into the circula- 
tion. 

In the production of heat and motion the carnivorous 
animal consumes itself, and, through the oxidation in- 
cessantly going on by means of the air introduced by 
respiration, carbonic acid, ammonia, water, sulphuric 
and phosphoric acids are constantly forming. 

On a superficial view it might be supposed that in 
the other group, the herbivorous, the case is quite dif- 
ferent. These seem to spend all their lives in obtaining 
food. The ox or the horse, put out to pasture, is all the 
day long cropping the grass. On a comparison of the 
quality and nature of the food they take with the sub- 
stance of which their bodies consist, there seems to be 
nothing in common. It was not, therefore, without rea- 
son that the earlier physiologists imputed to the digest- 
ive organs of this class the power of forming flesh and 
blood from vegetable matters. When, however, we 
come to a critical examination of the facts, we find that 
there is no essential difference between them and the 
carnivora. 

When the expressed juice of vegetables is permitted 
to stand for a time, though it may have been clear at 
first, a turbidity sets in, and a flaky material is deposit- 
ed. The substance thus possessing the power of spon- 
taneous coagulation is identical in that property, and in 
composition, with animal fibrin. Alter its deposit, if 
the clear liquid be wanned to near the boiling point, it 

How do these groups differ u their digestive apparatus? 

.' does the carnivorous animal produce heat? How is tho nutri- 
tion of herbivorous animals accomplished ? What effects occur spon- 
taneously in vegetable jui 



24 NUTRIENT MATTERS PRE-EXIST IN PLANTS. 

again becomes turbid, and a second nitrogenized sub- 
stance subsides, which, from its quality of coagulating 
by rise of temperature and its analysis, is inferred to be 
identical with animal albumen. When this has been 
separated by filtration or otherwise, and the juice is 
slowly evaporated, there come on its surface skins of a 
body having the same qualities as casein ; so fibrin, al- 
bumen, and casein pre-exist in plants. 

Fatty matters of every description may also be ex- 
tracted from vegetable products. From leaves, seeds, 
bark, wood, etc., oleaginous bodies can be obtained by 
the action of sulphuric ether. This liquid has the prop- 
erty of dissolving fat, and leaving it on subsequent evap- 
oration. 

It being thus understood that the food of the herbiv- 
orous animals contains nitrogenized bodies and fats 
ready formed, we have clearer views of the function of 
digestion in those tribes. It is not necessary to impute 
to their digestive organs the power of creating flesh 
and fat from vegetable matter. The office of the ani- 
mal is merely to collect. The two groups being com- 
pared together, the carnivorous animal receives under 
less compass the required amount of nutriment, and its 
digestive apparatus is more compact. But the herbiv- 
orous animal must all the day long collect large quan- 
tities of food, out of which it may extract the little nu- 
trient matter they contain. The carcass of an animal, 
seized by a lion, is almost all digestible, but it would re- 
quire a very large amount of herbage or of grain to be 
supplied to an ox to make up the same quantity of albu- 
men or fat. Hence the necessary complexity and size 
of the digestive organs of the herbivorous group, and 
hence many of their habits of life. 

Universal experience, as well as direct experiment, 
proves that in the case of man health can not be main- 
tained on a uniform diet, however it may be with ani- 
mals. A mixed food, changed from time to time, seems 
to be essential. 

What effects occur on heating vegetable juices ? What on evap- 
orating them ? Do fats pre-exist in vegetable products ? Describe 
the sources from which herbivorous and carnivorous animals respect- 
ively obtain their food. What is the cause of the difference of their 
digestive apparatus ? 



NECESSITY FOR MIXED FOOD. 25 

Undue excesses of albumen, oil, or starch, in the diet 
of an individual, produce a liability to arthritic, bilious, 
and rheumatic affections. An abstinence from fresh 
vegetables and fruits develops scorbutic, and a deficiency 
of oleaginous materials scrofulous disease. It is evident 
that a control over these affections may be obtained, or 
even their cure, to a considerable extent, accomplished, 
by suitable changes in the nature of the food. This is 
strikingly seen in the improvement of the health of sail- 
ors during long voyages, since the introduction of veg- 
etable preparations or acid juices. In 1726, Admiral 
Hosier sailed from England to the West Indies with 
seven ships of the line, and lost his whole crew twice by 
scurvy. The circumnavigation of the globe is now oft- 
en accomplished without the loss of a single man. 

Tables of the value of food, as dependent on chemical 
composition, are of little use in the case of man. The 
art of cooking does not minister alone to the gratifica- 
tion of the palate, it lends a real assistance to the oper- 
ation of digestion. New elements may not have been 
added, nor existing ones removed in submitting the food 
to the action of a high temperature, yet such a change 
is thereby impressed upon it that it becomes more capa- 
ble of digestion, and more subservient to the wants of 
the economy. 

Why is there a necessity for the use of mixed food ? What is the 
rhvsiological effect of cooking ? 

B 



26 ABSORPTION OF FOOD. 



CHAPTER III. 

OF DIGESTION. 
TISSUE-MAKING OR HISTOGENETIC DIGESTION. 

Nature of Digestion. — The digestive Tract. — The 
Mouth, Teeth, Stomach. — The Salivary Glands. — 
Different Kinds of Saliva. — Properties of mixed Sa- 
liva: its Quantity, Composition, and Functions. — 
The Stomach. — Gastric Juice. — Organs for its Prep- 
aration. — Manner of producing Chyme. — Influence 
of the Nerves. — Artificial Digestion. — Preparation 
and Properties of Pepsin. — Regional and functional 
Divisions of the Stomach in Animals and in Man. 
— Object of Stomach Digestion. — Peptones. — Use of 
Salt.- — Digestibility of various Articles of Food. 

Before the food can be absorbed and carried to all 
parts of the system it must be submitted to certain pre- 
paratory operations. It is necessary to bring it into a 
condition of solution in water, or at least into a state of 
minute suspension in that liquid. Received in masses 
of a certain size, it is first cut and crushed into smaller 
portions by the teeth, and then brought from an insolu- 
ble into a soluble or suspended state by the chemical 
action of the digestive juices. 

CONSTRUCTION OF THE DIGESTIVE APPARATUS IN MAN. 

The digestive tract may be considered as presenting 
six prominent regions — the mouth, the pharynx, the 
cesophagus, the stomach, the small intestine, the large 
intestine. Their relative position and subdivisions are 
illustrated in Figure 1. — 1, the tongue; 2, 2, the phar- 
ynx ; 3, 3, the cesophagus ; 4, the velum pendulum pa- 
lati ; 5, section of the larynx ; 6, the palate ; 7, the epi- 
glottis ; 8, the thyroid cartilage ; 9, the medulla spinalis ; 
10, 10, bodies of vertebrae; 11, 12, spinous processes of 

To what operation must the food be submitted before it can be 
absorbed ? Into how many regions may the digestive tract be di- 
vided? Describe Figure 1. 



ditto; 13, cardiac or- 
ifice of stomach ; 14, 
splenic extremity ; 
15, pyloric extrem- 
ity; 10, 10, greater 
curvature ; 17, the 
less curvature; 18, 
pylorus ; 19, superi- 
or transverse por- 
tion of duodenum ; 

20, middle or per- 
pendicular portion ; 

21, inferior trans- 
verse portion ; 22, 
gall-bladder; 23, cys- 
tic duct ; 24, hepat- 
ic duct ; 25, ductus 
communis choledo- 
chus ; 20, its aper- 
ture in the duode- 
num ; 27, duct of 
the pancreas, emp- 
tying into the duo- 
denum near to the 
place of entry of 
the ductus commu- 
nis choledochus; 28, 
commencement of 
jejunum; 29,29,29, 
jejunum; 30,30,30, 
ileum ; 31, ileum 
opening into great 
intestine ; 32, ileo- 
colic valve ; 33, ileo- 

•al valve; 34, cae- 
cum ; 35, appendix 
vermiformis; 30,36, 
the ascend in g colon; 
. transverse arch 
of colon ; 38, de- 
scending colon ; 39, 

moid flexure; 40, 
rectum ; 41, anus. 



HUMAN DIGESTIVE TRACT. 

Fig. 1. 



27 




The human digestive tract. 



28 



THE TEETH. 



Fig. 2. 



MECHANICAL ACTION OF THE MOUTH. 

In the mouth the food is submitted to a twofold prep- 
aration. It is divided by the mechanical action of the 
teeth, and also simultaneously mingled with liquids se- 
creted from the salivary glands. 

In man the number of temporary teeth is twenty, ten 
in each jaw. They are arranged in three classes — four 
incisors, two canines, and four molars for the upper and 
lower jaw respectively. The permanent teeth, eventual- 
ly substituted for these temporary ones, are thirty-two 

in number, classified 
for each jaw as four 
incisors, two canines, 
four bicuspids, and 
six molars. Their ar- 
rangement is exempli- 
fied in Fig. 2, repre- 
senting the lower jaw, 
in which i is the mid- 
dle and lateral incisor, 
c the canine, b the two 
bicuspids, and m the 

The human lower jaw. three molars. 

The movements of the teeth, aided by those of the 
tongue, accomplish a due abrasion of the food, and si- 
multaneously incorporate it with the saliva. This is, 
therefore, a purely mechanical operation. It is analo- 
gous to the methods resorted to by chemists in their 
laboratories when they prepare solid materials for ex- 
posure to reagents. 

INSALIVATION. PREPARATION AND USES OF SALIVA. 

Three pairs of glands, the parotid, submaxillary, and 
sublingual, secrete saliva. Of these organs the parotid 
is the largest ; its secretion is delivered through the 
duct of Steno. The submaxillary duct is Wharton's, 
but the sublingual pours its fluid through many small 
apertures. Besides these proper salivas, the lining 

To what preparation is the food submitted in the mouth ? What 
is the number of temporary teeth in man ? Into what classes are 
they divided? What do the teeth accomplish besides the abrasion 
of the food ? How many glands prepare saliva ? 




DIFFEKENT KINDS OF SALIVA. 29 

membrane of the mouth yields a fluid, the buccal mu- 
cus. 

The parotid saliva is thin and watery, limpid and col- 
orless, inodorous and tasteless. Secreted during fasting, 
or under the use of stimulating food, it is denser. It 
contains so large a quantity of lime that, on exposure to 
the air, it becomes covered with an incrustation of the 
carbonate of that substance. It also contains sulpho- 
oyanide of potassium. Its organic ingredient, if not al- 
buminate of soda, closely resembles that body. 

From the chemical constitution of the saliva of the 
parotids, the physiological function of those glands, as 
water-supplying organs, is established. They yield a 
certain quantity of watery juice, which, by reason of its 
thinness or fluidity, is readily incorporated with the food 
by the teeth. Parotid saliva appears to have no power 
of transmuting starch into sugar. 

The submaxillary saliva is also colorless and limpid, 
tasteless and inodorous. It is lighter than the parotid, 
less alkaline, and contains less lime. For this reason, 
when exposed to the air, it does not become incrusted 
with carbonate of that earth. It contains sulphocyan- 
ide of potassium. It is so viscid and glutinous that it 
may be drawn into threads. From this physical prop- 
erty it probably facilitates deglutition by furnishing a 
kind of anti-friction coating. 

The sublingual saliva is thin and watery, containing, 
like the parotid, but a small percentage of solid matter, 
and probably discharging a similar function. 

Besides the special salivary juices, the lining mem- 
brane of the mouth pours forth a liquid — the buccal 
mucus — a thick and tenacious substance. It is alkaline 
in its reaction, does not coagulate on heating, its insolu- 
ble salts containing no carbonate of lime. It has been 
obtained for examination by tying the ducts of Steno 
and Wharton, keeping the nostrils open and the head 
inclined, so that, the animal being unable to swallow, 
the mucus flows oat of the mouth. 

The buccal mucus, it' mixed with parotid saliva, does 
not appear to p the power of turning starch into 

What arc the properties of parotid saliva? What arc those of the 
submaxillary? What are those of the sublingual ? What are those 

of buccal mucus ? How do these juices respectively act on starch ? 



30 PROPERTIES OF MIXED SALIVA. 

sugar, but, if mixed with the submaxillary secretion, it 
accomplishes that transmutation with facility. 

The saliva, as obtained from the mouth, is therefore a 
mixture of the secretions of the various salivary glands. 
It is an alkaline juice, of a bluish color or colorless, in 
consistency glairy, readily frothing, and therefore well 
adapted for entrapping atmospheric air. It contains, 
of solid matter, from 0.348 to 0.841 per cent. Its alkali 
appears, for the most part, to be combined with an or- 
ganic substance, ptyaline. 

On standing, saliva separates into two layers ; a trans- 
parent one, which is supernatant, and a grayish turbid 
one below. Its chemical reaction varies to some extent 
with the state of the system ; thus, after long-continued 
fasting, from being alkaline, it may approach the neutral 
state. 

The specific gravity of mixed saliva varies from 
1.004 to 1.009. These variations depend on many dif- 
ferent causes, there being a diminution after the taking 
of drink, and a greater increase after taking food, than 
even is observed in the fasting state. An animal diet 
especially increases it. 

Under ordinary circumstances, the saliva is secreted 
to an amount of from 15 to 20 ounces daily. The exu- 
dation is more copious during mastication, speaking, 
reading, more being produced by the use of hard than 
soft food. Mental emotions exert a control over its 
flow, sometimes diminishing it, as in moments of anxie- 
ty, sometimes increasing it, as by the anticipation of 
food. After eating, the flow continues to a considera- 
ble extent ; it is also provoked by the use of aromatics. 
On irritation of the interior of the stomach through a 
gastric fistula, the flow is simultaneous with that of the 
gastric juice. 

The movements of the jaw and the pressure of the 
food give rise to variations in the quantity of saliva. It 
is perhaps for these reasons that the parotid gland on 
that side of the mouth which is most used in mastica- 
tion secretes more than the other. Of the proportion 

What are the properties of mixed saliva? What is ptyaline? 
How much saliva is secreted in a day? What circumstances exert 
a control over its flow ? Do both the parotids commonly secrete the 
same amount ? 



CONSTITUTION OF SALIVA. 31 

of the different kinds of saliva in the mixed secretion, 
nothing is known with certainty in the case of man, but 
it is said that in horses the parotids furnish two thirds, 
the submaxillaries one twentieth, and the sublinguals 
and mucous follicles the rest. The secretion of the sa- 
liva goes on during sleep. 

Constitution of Saliva. 

Water 994.10 

Epithelium and mucus 2. 13 

Fat 07 

Ptyaline and alcohol extract 1.41 

Sulphocvanide of potassium 10 

Fixed salts 2.19 

1000.00 

Of the fixed salts the chief are, the phosphates of soda, 
lime, and magnesia, and the chlorides of sodium and po- 
tassium. The snlphocyanide of potassium varies in 
amount considerably : it increases after meals, and es- 
pecially after the use of condiments, salt, pepper, spices, 
Those articles which contain sulphur, as mustard, garlic, 
radishes, increase its amount in a very marked manner. 

Not only does the saliva, as derived from the differ- 
ent glands, present differences of constitution ; it like- 
wise differs in various animals, and in the same animal 
according to its age. This is observed even in the case 
of man. The saliva of an infant at the breast possesses 
very little power of saccharizing starch, a transmutation 
which that of the adult accomplishes with energy. 

The action of this secretion appears to be limited to 
starch, and certain kinds of sugar, which first yield lac- 
tic and then butyric acid. It does not exert any influ- 
ence in transforming albuminous matter. 

The saliva discharges many functions. It acts as an 
anti-friction coating to the food descending into the 
stomach. It is a necessary intermedium in the sense of 
taste, for substances to be sapid must be more or less 
soluble in this juice. If insoluble, they are tasteless. It 
ns the interior of the mouth, and prevents 

What proportion i> furnished by each of the glands respectively ? 
What are the chief fixed salts of the saliva? What substances in- 
crease the amount of snlphocyanide ? What is the effect of infant 
and adult saliva on starch? Describe the general functions of sa- 
liva. 



32 SALIVARY DIGESTION IN THE STOMACH. 

the sensation of dryness. But its chief duty seems to 
be that of promoting the digestive operation ; for, though 
the food remains in the mouth but a short time, the ac- 
tion of the saliva is prolonged after the masticated mass 
has been deposited in the stomach. Though the direct 
admixture of saliva with gastric juice injures the power 
of the latter, this effect does not ensue in the stomach, 
since they act for the most part separately. The action 
of the gastric juice is superficial, and two distinct opera- 
tions are therefore conducted at the same moment, the 
surface of the food changing under the influence of the 
gastric juice, and the inner portion under that of the 
saliva. I believe that in this manner the salivary juice 
lends itself to stomach digestion, for by its aid starch 
changes into grape sugar, and the transmutation does 
not stop at that point, but goes on to the production of 
lactic acid. An acid juice is essential to stomach diges- 
tion. 

It has been suggested that the eventual arrest of the 
action of saliva on reaching the stomach may be due to 
the digestion of its ptyaline by the gastric juice. 

The double digestion, partly salivary and partly gas- 
tric, occurring in the stomach, is doubtless one of the 
causes of those differences noticed between the natural 
action of that organ and the artificial imitations of it. 
The influence of the saliva, even under these, which may 
seem at first sight to be unfavorable circumstances, is 
far from being trivial, an effect well illustrated by the in- 
stantaneous manner in which a solution of starch in wa- 
ter, mixed with an equal quantity of saliva and agitated, 
is transmuted into a solution of sugar. In a few mo- 
ments its viscidity is lost, it fails to give the blue reac- 
tion with iodine, becomes sweet to the taste, and readi- 
ly answers to Trommer's test. 

Besides the duties mentioned, the saliva incidentally 
accomplishes a secondary object by its power of retain- 
ing gases in its froth or foam. Atmospheric oxygen by 
this means is incorporated with the food during masti- 
cation, and is thus enabled to exert an important influ- 

In what manner is salivary digestion continued in the stomach ? 
In what manner is it possible that salivary digestion is arrested in the 
stomach? How may the influence of saliva on starch be tested? 
What is the use of the air carried by insalivation into the stomach ? 



JHGESTION IN FISHES. 33 

cnce in promoting the action of the gastric juice. For 
to the inception of the change which that juice impress- 
es on the food, oxygen is necessary. It is brought into 
the cavity of the stomach entangled or dissolved in the 
saliva. 

It has just been mentioned that the action of saliva 
on starch is not restricted to the production of sugar, 
but that it may end in the formation of lactic acid. If, 
therefore, any thing intervenes to check the supply of 
hydrochloric acid, which usually gives acidity to the 
gastric juice, the system possesses within itself the 
means of compensating for the difficulty. In the inte- 
rior of the digesting mass lactic acid is being set free. 
This acid, as has long been known, can replace hydro- 
chloric acid in its physiological duty. 

Since fishes and water animals generally have no sal- 
ivary glands, or only rudimentary ones, some physiolo- 
gists have inferred that the use of the saliva is for the 
commingling of the food with a due portion of water. 
This would reduce the importance of insalivation very 
greatly, and, indeed, is scarcely consistent with the elab- 
orate mechanism of ruminant animals. It is w T orthy of 
remark that, even among fishes, there are some which 
exhibit a true rumination, as, for example, the carp. 
This is not alone for the purpose of resubmitting the 
food to the abrading action of the pharyngeal teeth, but 
likewise for commingling it with the secretion of the 
pharyngeal cavity. 

.Among the functions of the saliva we ought not to 
overlook the influence its rapid secretion must exert on 
the state of tension of the blood-vessels, an influence 
which probably favors the absorption going on in the 
stomach and intestines. 

DIGESTION IN THE STOMACH. 

Thus prepared by mastication and insalivation, the 
food descends into the Btomach, passing along the phar- 
ynx, whirh dilates to receive it. The lima glottidis 
spontaneously closes, and additional security is given to 

What acid ma; ally produced by the saliva from starch ? 

what purpose U it that certain fishes ruminate? How is the 

condition of the blood-vessels affected \>y t lie secretion of saliva ? 
.ribe the passage of the food through the oesophagus. 

j; 2 



34 - THE STOMACH, 

the respiratory passage by the valve-like shutting of the 
epiglottis. Through the oesophagus the morsel advances 
by the contraction of the muscular coat, with a wave- 
like or undulating motion onward. The food is now 
delivered at the cardiac orifice of the stomach, and, en- 
tering that organ, is submitted to the gastric juice ex- 
uding from the mucous membrane. 

The stomach is an expansion of the alimentary canal 
between the oesophagus and the duodenum, of a conical 
figure, the base to the left. It communicates with the 
oesophagus by its cardiac orifice, and by its pyloric with 
the duodenum. It consists of three coats or tunics — 
the serous or peritoneal, which is exterior ; the muscu- 
lar, which is intermediate ; and the mucous, which is in- 
terior. They are connected with each other by cellular 
tissue. The fibres of the muscular coat run in three 
different directions, constituting three layers ; the su- 
perficial ones are longitudinal, radiating from the oesoph- 
agus over the surface of the organ; those of the middle 
layer are circular, or ring-like ; they are well developed 
about the middle of the stomach, and by their contrac- 
tions sometimes make it assume a divided appearance, 
as though composed of two compartments. Toward 
the pylorus they are also greatly re-enforced. The 
fibres of the third layer take, for the most part, an ob- 
lique direction. The interior or mucous coat is some- 
times termed the villous, from its velvety appearance. 
Its color is very variable ; it is folded into rugse, admit- 
ting of variations in the distention of the stomach, with- 
out interference with the structure or functions of the 
membranes of which they are a part. The cardiac ori- 
fice is plicated, and the opening into the duodenum is 
through a circular fold with a central aperture — the py- 
loric valve, which being surrounded with a band of mus- 
cular fibres acting as a sphincter, the passage from the 
stomach to the intestine may be entirely obstructed. 

The stomach is seen in section Fig. 3, a being the 
oesophagus ; 5, the greater extremity ; c, the smaller 
curvature; <#, the -great curvature; 6, the pyloric or less 
end ; /*, A, the duodenum ; g, place of entry of the duc- 

What is the general shape of the stomach ? How many coats has 
it ? Describe each of them. Describe the parts shown in Fig. 3. 



THE STOMACH. 

Fig. 3. 



35 




Section of the human stomach showing its mucous interior. 

tus communis choledochus and pancreatic duct. The 
place of junction of the oesophagus is the cardiac region : 
the membrane is there plicated. The place of junction 
of the duodenum is the pyloric region. 

The typical form of the digestive apparatus is a sac 
with one aperture, serving the double purpose of afford- 
ing an entrance to nutritive material, and an outlet to 
undigested remains. In a higher condition it may be 
conceived of as a tube open at both ends, and having a 
sac-like swelling on its middle part. The portion of 
the tube anterior to the sac is the type of the oesopha- 
gus, its aperture answering to the mouth, the sac-like 
swelling being the type of the stomach, and the tube 
leading from it representing the intestinal canal. In 
the more elementary of such forms, vessels arise from 
the walls of the digestive cavity,, and pass to all other 
parts of the system. These serve to convey the elab- 

ited material. Certain appendages are soon to be 
discovered in connection with this simple digestive 
mechanism. They are for the preparation of salivary, 

itric, pancreatic, or biliary juices. Tn size or devel- 
opment they vary with the habits of life of the animal, 
or with the nature of its food. Indeed, the same re- 
mark may be made -ts the entire digestive tract 

What i< the typical form of the digestive apparatus? How does 

it gradually become more complex? What appendages to it are 
gradually provided ? 



36 THE GASTRIC JUICE. 

of the highest tribes. Thus, in the bat, the length of 
the intestine is to that of the body as three to one, but 
in the sheep as twenty-eight to one. The ruminants 
generally have an intestinal tube of great length. In 
man and in monkeys the proportion is about five or six 
to one. Again, as regards construction, there a»re many 
diversities, the number of digestive dilatations and their 
size corresponding in some measure to the nature of the 
food. 

The interior of the stomach is of a light pink color, 
its velvety surface being coated over with mucus. On 
the introduction of food or any irritant, lucid points pro- 
trude from the mucous coat ; these are the mouths of 
the follicles from which the gastric juice exudes. When 
in activity, the temperature of the interior of the organ 
is about 100° Fahr. 

The gastric juice is a viscid fluid, with an acid reac- 
tion and faint odor. After filtration through paper it 
is clear and transparent, and possesses all its physiologi- 
cal qualities. The impurities thus separated from it are 
merely old undigested residues, on which, in no respect, 
its qualities depend. It does not become turbid at 212°, 
remains long undecomposed, and retains its digestive 
power even after it has become mouldy. It does not 
accumulate in the stomach while fasting, but requires a 
stimulus for its ejection, and even then is produced in a 
limited quantity only. It is secreted by the follicles of 
the mucous membrane of the stomach. They are cup- 
shaped cavities, about the two hundredth of an inch in 
diameter, from the bottom of which project two or more 
parallel tubes, the mouth of the cup opening into the 
stomach, and the tubes ending in a closed termination 
in the tissue beneath. Toward the pylorus the cups be- 
come deeper, so as to assume the form of a cylinder, 
and the projecting tubes are shorter. Between these 
follicles blood-vessels pass. 

Nearly two thirds of the solid material of the gastric 
juice is pepsin. Exposure to a very low temperature 
does not deteriorate the properties of this substance, 

What is the appearance of the interior of the stomach ? What is 
its temperature ? Describe the gastric juice. How is it secreted ? 
In what manner are the blood-vessels related to the follicles ? What 
are its properties ? 



STOMACH FOLLICLES. 



for it will resume its activity even after being frozen. 
But, on the contrary, a temperature approaching ebulli- 
tion destroys its solvent power, and the same effect en- 
sues when it is neutralized by an alkali. 

The digestive power of this juice is impeded by the 
presence of almost any alkaline salt. It is owing to its 
alkalinity that saliva injures the di- Fig. 4. 

ing power of gastric juice. On 
the contrary, that power is very 
much increased by the presence of 
fat, which promotes the conversion 
of protein bodies into peptones. 

In F'kj. 4 is a representation of 
stomach follicles and their tubes in 
a vertical section. The specimen 
is from the dog after twelve hours' 
fasting. A represents these struc- 
tures in the middle region of the 
stomach ; B in the pyloric region ; 
<' ", oritices of the follicles on the 
inner surface of the stomach ; b b, 
different depths at which the co- 
lumnar epithelium is exchanged for 
glandular ; d, pyloric tubes termina- 
ting variously, and lined to their ex- 
tremities With Columnar epithelium. Vortical section of stomach 

There are therefore two distinct *>"**£ * m<1 *■*" m;l - nU 

, n i/*iti -i • nn • fied 15 ° diameters. 

classes of stomach follicles, differing 
from each other in anatomical construction, and, as 
there is now reason to believe, also in physiological 
function. It is suspected that the acid of the gastric 
juice is prepared by one class of these structures, and 
the pepsin by the other. 

Though we have spoken of the follicles as excavations 
or cup-like depressions in the mucous tissue, according 
ription usually given of them by anatomists, 
it is to be understood that this view of their construc- 
tion is philosophically incorrect, for each, instead of be- 

What it the effort of an alkaline salt on it ? What is the effect of 

fat? Describe the stomach follicles shown in Fig. 4. How many 
macfa foil* there? What are their supposed 

functions? In what respect is the construction of the stomach hv- 
droid? 





38 STRUCTURE OF THE STOMACH. 

ing a mere excavation, is truly a distinct organism, an- 
alogous in structure and many of its functions to a pol- 
g ype. The hydra, 

a fresh- water pol- 
ype, may be tak- 
en as the type of 
this organism. 
This animal, Fig. 
5, consists of a 
bag or digestive 
sac, a a, ending 
•in a cylinder, 5, 
the opening to 
which is furnish- 
ed with numer- 
ous tentacles, c c 
c; the tentacles 
enfold in their 
grasp objects on 
which the hydra feeds, and by their contractions carry 
them to the sac. Into the interior of the sac a juice 
exudes possessing digestive powers, and soon dissolving 
food. 

We may therefore regard the follicular structure of 
the stomach as a colony of polypes, the tentacles of 
which are converged into a muscular tube, constituting 
the oesophagus. In a stomach of ordinary size there 
are probably a million of these organisms. Digestion 
is undoubtedly conducted on the same physical princi- 
ples in both cases, though in the polype the food matter 
enters the follicular cavity of which the body of the ani- 
mal consists, but in man is contained in the stomach, 
into which the follicles open, and pour forth their di- 
gestive fluid. 

With respect to the acid constituent of the gastric 
juice, it is hydrochloric or lactic. The latter has prob- 
ably originated in the manner just described by the ac- 
tion of the saliva on starch ; the former undoubtedly 
comes from the common salt ingested. Perhaps, under 
a deficiency of common salt, lactic acid discharges the 

Describe Fig. 5. What is the oesophagus? What is the acid 
constituent of the gastric juice ? 



BUMMABY OF STOMACH DIGESTION. 39 

entire duty. About twenty parts of gastric juice are 
required to digest one part of dry albumen, and about 
TO ounces are secreted in a day. If the hourly destruc- 
tion of fibrin in average muscular action is 62 grains, 
about GO ounces of gastric juice would be required each 
day for muscular repair. A very large demand is there- 
fore made upon the water in the system for this use. 
But here the same remark occurs as in the case of the 
saliva ; the water, after accomplishing its object, is not 
lost to the economy, but is immediately reabsorbed. 

On ihe deposit of the food in the stomach, a move- 
ment of translation is given to it by the alternate con- 
traction and relaxation of the fibres of the muscular 
coat, aided to a considerable extent by the respiratory 
movements of the abdominal walls. The course of this 
rotation commonly is, that after passing the cardiac ori- 
fice the food moves from right to left round the great 
extremity, and then along the large curvature from left 
to right, returning along the small curvature, and occu- 
pying from one to three minutes to perform this revolu- 
tion, the motion continuing for a few minutes at a time. 

While this is going forward digestion is rapidly tak- 
ing place, and the portions that have suffered complete 
action are oozing through the pyloric valve into the 
intestine as a semi-fluid and apparently homogeneous 
material called chyme. This process has fairly set in in 
the course of an hour, and is usually finished in about 
four. In consistency, color, and chemical reaction, the 
chyme varies with the nature of the food, its chemical 
constitution, and its quantity. 

EXPLANATION OF GASTRIC DIGESTION. 

B h is the general description of the act of diges- 
tion. We have next to enter on a physical examination 
of what it is that really takes place in the stomach. It 
was formerly supposed that digestion is entirely due to 
nervous agency, since, if the pneumogastric nerves be 

much of that juice ifl provided each day ? What U the hour- 
ly destruction of fibrin? Describe the movements the food nnder- 

8 in the stomach. How long does each rotation require? De- 
scribe the appearance and formation of chyme. Throngo what valve 
does the chyme pass ? Do the nerves exert any influence in diges- 
tion ? 



40 ARTIFICIAL DIGESTION. 

divided, the process is very much interfered with. But 
this interference takes place only in an indirect way, for 
the division of those nerves is attended with such a par- 
alysis of the stomach that those movements which so 
well serve to mix up the food with the gastric juice, 
and expel it through the pyloric valve, are put an end 
to. 

The acidulating material of the gastric juice is hydro- 
chloric acid. Is it possible by artificial mixtures con- 
taining that substance to reduce food articles to a di- 
gested condition? This inquiry introduces a descrip- 
tion of the experimental investigations which have been 
made in artificial digestion. 

When water acidulated with hydrochloric acid is kept 
in contact with albumen, no action is perceptible at or- 
dinary temperatures in a moderate period of time. If 
the temperature is raised to about 150° a slow dissolu- 
tion ensues, which becomes better marked as the heat 
rises toward 212°. 

But if to the weak hydrochloric acid thus made to 
act on albumen, pepsin is added, the solution takes place 
with rapidity at moderate temperatures. An ounce of 
water, mixed with twelve drops of hydrochloric acid to 
which one grain of pepsin has been added, will com- 
pletely dissolve the white of an egg in two hours at a 
temperature of 100°. It acts in the same manner on 
cheese or flesh, these nitrogenized articles being con- 
verted into soluble non-coagulable bodies. The acid 
does not enter into chemical combination with the dis- 
solving organic matter. It may be recovered from the 
solution by resorting to proper processes. 

Pepsin — the substance resorted to in these experi- 
ments — may be obtained by macerating the mucous 
membrane of the stomach for a short time in lukewarm 
water. This water, along with a part of the pepsin, re- 
moves various impurities ; it may therefore be cast 
away ; the maceration being then continued with a fresh 
portion of cold water, and this being submitted to filtra- 
tion, and subsequently evaporated at a low temperature 
to dryness, yields the pepsin as a gummy mass. 

In artificial digestion, what is the action of hydrochloric acid ? 
What occurs on the addition of pepsin ? Describe the preparation 
of that body. 



FUNCTIONS OF PEPSIN. 41 

Its analysis indicates that pepsin contains less carbon 
and more nitrogen than the members of the so-called 
protein group. 

A weak acid therefore possesses at a high tempera- 
ture the power of bringing into a state of solution the 
various nitrogenized food matters, and at lower degrees 
fails of that property; but in the presence of pepsin the 
solvent powers are assumed under the latter circum- 
stances, and therefore it is said of this substance that it 
replaces a high temperature. By its aid, hydrochloric 
or lactic acids present in the stomach reduce the food 
to a uniform pulpy mass — the chyme. 

Formerly it was supposed that the act of digestion 
was simply mechanical, the food being ground down to 
chyme by the motions of the stomach. Reaumur's ex- 
periments showed the error of this supposition. He 
took small hollow silver balls, perforated with holes, 
and, having filled them with meat, caused them to be 
swallowed by a dog. When they had remained in the 
animal's stomach a suitable length of time, they were 
withdrawn by a thread previously attached to them. 
Xow if the stomach acted by a triturating or grinding 
power, the material within the ball would be entirely 
protected, but if by a solvent power exerted by the gas- 
tric juice, the digestion should at most be only delayed. 
Accordingly it was found that this was what actually 
took place, digestion being fully, though more slowly 
accomplished, the action commencing on the outside of 
the material, and gradually reaching its centre. If the 
balls were kept in the stomach long enough, they came 
out quite empty at last. 

The idea that some mysterious change is impressed 
upon the food by the vitality of the stomach may there- 
fore be abandoned. It does not appear that there is 
any essential difference between natural digestion and 
the artificial imitation of it, either as respects the order 
of action or the final result. Moreover, the anatomical 
aideratioD that the food is yet outside the body, 
though it is inside the stomach, should be sufficient to 

How does it stand related to the protein group? In whal manner 
may it 1>^ said to replace a high temperature? Describe the experi- 
ments of Reaumur. What is the final object of digestion ? Does the 
food acquire any vital properties in the stomach? 



42 OBJECTS OF DIGESTION. 

remove all errors of that kind. A living surface, such 
as the skin, never exerts any chemical action at a dis- 
tance; and the lining membrane of the stomach, both as 
regards its physiological origin and its anatomical rela- 
tion, is nothing more than a reflected continuation of 
the skin. The act of digestion is completed long before 
the nutrient material is absorbed and thrown into the 
torrent of the circulation. But then, and not till then, 
is the food fairly in the interior of the body. 

Digestion is not, therefore, to vitalize the food, as the 
ancients supposed, nor to communicate to it any new or 
obscure properties ; it is for the purpose of comminu- 
ting, subdividing, dissolving, or bringing it into that 
minutely suspended state that it can without difficulty 
be absorbed by the lacteals and veins. There is a com- 
plete analogy between this operation and the artificial 
processes to which the chemist resorts in his laboratory 
for the solution of various bodies. He, too, uses me- 
chanical implements — the mortar and pestle to grind, 
the hammer to crush, the rasp to abrade. When these 
have carried the subdivision sufficiently far, he resorts 
to acids or other solvents, and thus breaks down the 
compactness of the hardest minerals, and brings them 
into the dissolved state. The animal world presents 
us with a thousand illustrations of the principles here 
set forth, mechanical contrivances curiously arranged. 
For instance, birds, whose plan of organization is such 
as to meet the case of locomotion through the air, could 
not have the anterior part of their bodies loaded with 
teeth, accompanied as they must have been with a pow- 
erful muscular apparatus. Such a mechanism would 
have rendered the animal top-heavy, and have been to- 
tally inconsistent with flying. But, to avoid this diffi- 
culty, that which might truly be regarded as the mouth 
is lodged in the interior of the body, nearer the centre 
of gravity. It is the gizzard. Instinct teaches the bird 
to swallow small angular stones ; they serve as tempo- 
rary teeth, and the food, rasped between powerful mus- 
cular surfaces, is soon brought into a fit condition for 
the action of the stomach. The chemist, too, puts frag- 
ments of glass or of quartz into the mortar in which he 

Is it illustrated by any artificial operations? What is the func- 
tion of t\e gizzard of birds ? 



OBJECTS OF DIGESTION. 



43 



Fig. 6. 



is conducting the reduction of a tough or resisting sub- 
stance. 

The first object of digestion is, therefore, the subdi- 
vision of the food. The operation begins in the mouth 
by a resort to mechanical implements, and when these 
have carried the process as far as they can, the stomach 
continues the duty. Iu its cavity, when in full activity, 
the temperature is 100° ; a periodically increasing and 
relaxing motion of revolution is kept up, gastric juice 
exudes in definite quantity, the hydrochloric and lactic 
acids exert their action, and in the course of three or 
four hours a complete reduction is accomplished. 

Allusion has been made to the probability that differ- 
ent portions of the mucous membrane of the stomach 
discharge functions wholly distinct, one portion being 
devoted to the elaboration of pepsin, another to the se- 
cretion of hydrochloric acid, another to the preparation 
of a special mucus. This view derives considerable 
support from many facts in comparative physiology. 
In those cases in which the food ap- 
proaches, in its mechanical and chem- 
ical condition, to the form which it is 
destined to assume as a part of the 
body of the animal receiving it, the 
stomach is simple in construction, and 
is little more than a mere dilatation 
of the alimentary canal. But when, 
as among the herbivora and granivo- 
ra, there is a great difference between 
the form of the food received and the 
form of the tissues to be made, the di- 
ive sac no longer presents such a 
simple structure, but is parted off into 
distinct regions, or is actually convert- 
ed into distinct organs. 

Tims, in the insect digestive tract 

shown in Ftg. 6, a is tin- pharynx, 1> 

the oesophagus, leading into a crop or 

. and tlii< into the 

ard, <K the function of which is to 

ion of the stomach. Does the entire 

interior - eh discharge cue functiun? Describe 

the regions indicated in J'iy. 6. 




i rar- 

dItov 



44 



DIGESTION IN INSECTS AND BIRDS. 



rasp up and abrade the more resisting portions of the 
food, which, when this is accomplished, passes into the 
true stomach, e y and Fiffm 7 

from thence into the 
intestine, #. The del- 
icate vessels about/* 
are supposed to be 
biliary tubes, and h 
glandular secreting 
organs. 

Even in these 
cases of minute or- 
ganization, the mu- 
cous structure re- 
mains the same as 
in larger animals of 
the same mode of 
life. The photo- 
graphic represeilta- Mucous membrane of the stomach of a carnivorous 

*-l * . -»-»• »- -i • hfip.il p. TYiRPTiifipri Kft rlinrnfiiprsi. 

tion in Jbig. 7 dis- 




Fig. 8. 



heetle magnified 50 diameters. 

plays the same reticulated ap- 
pearance in the stomach of 
the carnivorous beetle as de- 
scribed in the case of man ; 
and undoubtedly, with simi- 
larity of structure there is 
similarity in the manner of 
action. 

A regional division of the 
digestive apparatus is also 
presented in the case of many 
birds, as is shown in the pho- 
tographic representation,^'^. 
8, in which we have the di- 
gestive tract of the common 
fowl, a being the oesophagus 
leading into the insalivating 
pouch or crop, 5, which emp- 
ties into the stomach, o, and 
this into the gizzard, d. In 
the stomach, which is rela- 
Digestive tract of the common fowl, tively small, the digesting ma- 

What are the regional divisions in the digestive tract of a common 
fowl ? 




REGIONAL SUBDIVISIONS OF THE STOMACH. 



45 



Fig. 9. 



terial is mingled with the gastric juice before being sub- 
mitted to the action of the gizzard. From the gizzard 
it is passed into the small intestine/*,/*. In the figure, 
e is the liver, r/, r/, the cseca, and h the cloaca. 

In the ostrich, as shown 
in Fig. 0, the local distribu- 
tion of the glanduhv very 
obviously marks out a re- 
gional distribution of func- 
tion. C is the cardiac cav- 
ity, the mucous membrane 
of which is studded here 
and there with glands; G 
G are the surfaces of the 
gizzard. Among the high- 
er quadrupeds, the eviden- 
ces of a similar division of 
function are presented. 
Thus, in the dormouse, Fig. 
10, there are two compart- 
ments : a cardiac, C, and a 
pyloric, P; the same being 

exhibited more "perfectly in Interior of stomach of African ostrich. 

the Cape hyrax, Fig. 11. In these cases the cardiac 




Fig. 10. 



Fig. 11. 





r\ch of dormouse. 



Stomach of Cape hyrax. 



compartment is often lined with cuticle, but the pyloric 
not. An increase 10 the Dumber of these cavities oc- 
curs as the food becomes more heterogeneous. In the 
porcupine, Fig. 12, there are four, and in the porpoise, 

F'g. J 3, five. 

What principle is illustrated by the Figures from J) to 14 inclu- 
sive ? 



46 



DIGESTION IN RUMINANTS. 

Fig. 12. Fig. 13. 





Stomach of porpoise. 



Stomach of porcupine. 

The case of ruminants possesses a special interest. 
In these there are what might be termed four different 
digestive chambers, as is shown in Fig. 14, in which a is 




Digestive cavities of a ruminant. 

the oesophagus ; 5, the ingluvies or paunch ; c, the reticu- 
lum or honey-comb stomach • d, the omasum, manyplies, 
or third stomach ; 6, abomasum, reed, or fourth stomach ; 
andy, the pylorus. The food, roughly triturated in the 
mouth, enters the ingluvies, in which it is moistened ; 
it then passes into the honey-comb or second stomach, 
which likewise receives directly the water that has been 
taken, and, after it has been thoroughly moistened there- 
with, it is returned to the mouth in small quantities, to 
undergo a more complete mastication and insalivation. 
Being swallowed again, it is now directed into the third 
stomach, from which it passes into the fourth. In this 
it is submitted to a true acid digestion, a gastric juice 
being secreted from the walls of this cavity. It is the 
mucous lining of this cavity which yields rennet. That 

In ruminating animals how many digestive chambers are there ? 
What are the several uses of those divisions ? Which is the cavity 
that yields rennet ? 



PRODUCTION OF PEPTONES. 47 

these complicated motions and these successive actions 
of the different cavities are for the purpose of prepara- 
tion for the true digestion of the fourth stomach, is 
clearly proved by the fact that in the calf the milk pass- 
es directly into the abomasum. 

In view of the preceding facts, it may be concluded 
that, so far from there being any thing in contradictio: 
to the doctrine that different portions of the digestive 
surface of the mucous membrane of the stomach are de- 
voted to different duties, there is strong evidence in sup- 
port of its truth, derived partly from the instances fur- 
nished by comparative anatomy, and partly from the 
anatomical structure of the gastric mucous membrane. 
The four separate digesting chambers of the ruminating 
herbivora are merely an elaboration of the structure 
presented by an apparently homogeneous mucous sur- 
face in man. 

The gastric juice not only dissolves, but also, in an in- 
cipient and indirect manner, modifies the food. Protein 
bodies and gelatinous matters yield substances after its 
action of the same composition as their own, but with 
different physical and chemical properties, being readily 
soluble in water, and even in diluted alcohol, and not 
forming insoluble compounds with metalline salts. 
These substances have been designated as peptones ; 
and since they may arise without the evolution or ab- 
sorption of any gas, and the quantity of sulphur they 
contain is the same as that in the bodies from which 
they were derived, the action appears to be really an 
assimilation of water, the other ingredients remaining 
unchanged. 

It is interesting to observe the economical manner in 
which the hydrochloric acid element of the gastric juice 
tanaged. To the proper understanding of this, it is 
.rv to anticipate what will have to be more fully 
considered in describing the bile, a uniform ingredient 
of which is the oxide of sodium, or soda. The hydro- 
chloric acid of the gastric juice and the soda of the bile 
are derived from the same source — common salt, which 
is either present in the food, or purposely added as a 

Is there n rJODft] <livi-i<.ii> ndsl in the hu- 

man stomach? What are peptones? How is common salt used in 
digestion ? 



48 USES OF COMMON SALT. 

condiment. Salt undergoes decomposition easily, yield- 
ing the two products specified, that is, hydrochloric acid 
and soda, and is readily formed by the reunion of these 
substances. 

There exists in the action of the kidneys a special 
provision for preventing the quantity of chloride of so- 
dium present in the blood from rising over 41 parts in 
10,000. This, of course, controls the amount diffused 
through the tissues. The necessity of such a regulation 
becomes apparent when we consider that the rate of 
the solubility of albumen and casein in water is gov- 
erned by the presence of that substance, as is also the 
quickness with which the coagulation of fibrin takes 
place, and the repair of the waste of the muscles. 

Common salt introduced into the system undergoes 
decomposition, furnishing hydrochloric acid to the gas- 
tric juice, and soda to the bile. Considering the large 
quantity of these secretions produced in a short space 
of time, it is clear that the drain of common salt must 
be great — not less than a third of an ounce a day; yet 
the quantities consumed, at most, are only small. 

How, then, is this to be explained ? There is no oth- 
er source from which these bodies can come than the 
one indicated — the common salt, and yet it seems to be 
totally inadequate. 

This difficulty is rather imaginary than real. Things 
are so arranged that a limited quantity of salt can pro- 
duce unlimited quantities of gastric juice and bile; for 
the former, associated with the food it has digested, 
scarcely escapes from the pyloric valve before it encoun- 
ters the bile and pancreatic juices discharging into the 
duodenum, and through the length of the upper portion 
of the small intestines, these secretions, together with the 
food they have acted upon, are brought into complete 
contact. The reproduction of chloride of sodium is 
therefore constantly taking place in intestinal digestion, 
and it returns back to the system through the absorb- 
ents. Again it undergoes decomposition, its acid reap- 
pearing in the gastric juice, and its alkali in the pan- 
creatic juice and bile. By thus using a small amount 

How much of it may exist in the blood ? What substances does 
it yield by decomposition ? In what way may a limited quantity of 
it be sufficient ? 



SUMMARY OF DIGESTION. 49 

over and over again, great effects can be produced, and 
it is then only necessary to restore those small portions 
that are wasted in carrying out the general scheme. 

In the low-pressure marine steam-engine we have an 
example of the same kind. A certain quantity of water 
is vaporized in the boiler and condensed in the engine ; 
pumped back into the boiler to be vaporized, and then 
recondensed in the engine. Comparatively little is re- 
quired to supply the wants of the machine, and long- 
voyages can be made with only as much water as will 
compensate for the necessary waste arising in the work- 
ing. 

For the sake of presenting the consideration of the 
function of digestion with clearness, it is customary to 
leave out of consideration the subordinate actions tak- 
ing place both in the stomach and intestine. This, 
however, iuvolves a certain amount of error, since respi- 
ratory or non-nitrogenized digestion occurs in the for- 
mer cavity, and nutritive or nitrogenized in the latter. 
Nevertheless, there can be no doubt that if our view is 
restricted to the more imposing characters, we are jus- 
tified in accepting the dogma that " stomach digestion 
is histogenetic or nitrogenized, and intestinal digestion 
is calorifacient." 

Under the most comprehensive point of view, exam- 
ining the action of the entire digestive tract from the 
mouth to the rectum, we discover a recurrent periodici- 
ty. In the mouth, the transitory digestion taking place 
is wholly expended upon the calorifacient food ; in the 
stomach it is the nutritive portion which is chiefly at- 
tacked; in the duodenum there is a return to the ca- 
lorifacient, and in the ca?cum of animals a resumption 
of the nutritive. This last is less apparent in man, for 
in him the crecum exists only in a rudimentary state, 
represented by the appendix vermiformis. 

Intermediate between the classes of calorifacient and 

histogenetic food, belonging, by its composition and 

conditions of dig to the latter, but by the function 

it discharges to the former, is gelatine, a nitrogenized 

stance. It appears to bo always derived from albu- 

How is this illustrated by the steam-engine? What i< meant by 

the recurrent periodicity of digestion? In what manner does the 
enecum exist in man? 

c 



50 RELATIVE DIGESTIBILITY OF FOOD. 

men, and any portion which may have been received in 
the food is never directly assimilated or used for the 
fabrication of tissue, but solely ministers to the produc- 
tion of heat. Though thus a calorifacient body, its 
place of digestion is the stomach. After it has suffered 
the action of that organ it has lost its power of gelatin- 
izing, can no longer be precipitated by chlorine, nor 
give the leather precipitate with tannin. The use of it 
under the form of jellies, soups, etc., is always attended 
with the appearance of an unusual quantity of urea, and 
hence the administration of those domestic preparations, 
under an idea of their great nutritive value, is to be 
looked upon as only a popular error. In an indirect 
way, however, under the conditions of restricted diet, 
usually met with in the sick-room, gelatine doubtless 
maintains an interesting relation to the albuminoid 
bodies in this, that it protects them from destruction by 
undergoing oxidation itself, and so satisfying the re- 
quirements of the respiratory mechanism ; for, were 
there not such a substance present to receive the at- 
tack, the respired oxygen would rapidly bring on the 
waste of the proper nitrogenized tissues. 

Statements respecting the digestibility of different 
articles of food must be received with many restrictions. 
If, as the earlier physiologists believed, the stomach was 
the sole digestive cavity, and the intestine only for the 
purpose of absorption, they would doubtless be much 
nearer to the truth. But when we recall that the di- 
gestion of fats does not even begin until the intestine is 
reached, and that the digestion of the nitrogenized sub- 
stances is only in part accomplished by the gastric juice, 
but goes on under the influence of the intestinal juice 
throughout the whole length of the small intestine, we 
see at once how imperfect and even incorrect are the 
indications afforded by such experiments as those of 
Spallanzani, who introduced food articles into the stom- 
ach through the oesophagus in perforated silver vessels, 
or those of Beaumont, who availed himself of a gastric 
fistula. Neither can we take, in all instances, the time 

"What may be observed respecting the digestion of gelatine ? 
What uses does gelatine really subserve ? What circumstances in- 
terfere with estimates of digestibility ? What experiments were made 
by Spallanzani? 



RELATIVE DIGESTIBILITY OF FOOD. 51 

which an article of food will remain in the stomach as a 
measure of its digestibility, for this is known to vary 
with many conditions, as, for instance, the quantity in- 
troduced at a time, and the condition of the organ it- 
self. The white of an Qgg^ representing soluble albu- 
men, if introduced into the stomach of a fasting dog 
through a gastric fistula, will disappear in less than an 
hour; but if the whites of eight eggs be introduced, 
portions thereof can be recognized after four hours. 

JSo far as such examinations go, they do not exhibit 
any marked difference between albumen, fibrin, and ca- 
sein. Gelatine, however, is acted on with remarkable 
rapidity. The experiments which have been made on 
the digestibility of vegetable food introduced through 

itric fistuhe are obviously of no use, since the chief 
constituents thereof, such as starch and fat, are not even 
influenced in those circumstances until they have reached 
the intestine. Their passage from the stomach in this 
unchanged state, or changed only so far as their nitro- 
ized ingredients are concerned, may teach us the im- 
portant fact, which should in these inquiries be always 
borne in mind, that disappearance from the stomach is 
one thing and digestion another, and that even though 
a substance may have passed the pyloric valve, its di- 

-tion, far from having been completed, may not as 
yet have commenced. 

The digestion of nutritive or nitrogenized material — 
histogenetic digestion — is therefore carried on in the 
stomach mainly; and though first mechanical, and then 
mica] agencies are resorted to, the object is through- 
out the same — to obtain the food in such a divided and 
changed state that it can pass, dissolved in water, into 
the capillary 

dors the quantity of food affect these estimates? What food 
articles altogether escape digestion in the stomach? To what class 
the action of that organ restricted 



52 INTESTINAL DIGESTION. 



CHAPTER IV. 

OF CALORIFACIENT OR INTESTINAL DIGESTION. 

Nature of Intestinal Digestion. — Structure of the In- 
testine. — Digestive Fluids of the Intestine. — The 
Pancreatic Juice. — The Enteric Juice. — Juice of Lie- 
berkuhn. — Secretion ofPeyer's Glands. — Illustration 
of Intestinal Digestion from the making of Wine. — 
Making of Bread. — Influence of Heat over Ferments. 

— Comparison of Gastric and Intestinal Digestion. 

— Changes of the Intestinal Contents. — The Foecal 
Residues. 

After the chyme formed in the stomach has passed 
through the pyloric valve into the small intestine, the 
influence of the gastric juice continues for a certain 
time, even after the bile and pancreatic juices have been 
reached. Since their action must be necessarily, in the 
first instance, superficial, the interior of the mass is still 
undergoing stomach digestion. 

But, setting aside this incidental result, which at the 
most can not be of long duration, the digestive opera- 
tion taking place in the part of the intestinal tract now 
under consideration is upon the heat-making food. 

The organ in which calorifacient digestion takes place 
may be described as a tube bounded by two valves, the 
pyloric above and the ileo-caecal below. Its length may 
be estimated at about twenty feet. The digestive sur- 
face, making a due allowance for its increase by reason 
of its valvular structure presently to be described, can 
not be much under 3500 square inches. The dimen- 
sions of the calorifacient digesting surface are therefore 
far greater than those of the nutritive. 

The interior and acting portion of this tube presents 
two different systems of apparatus, and is occupied in 

Why is it that stomach digestion continues in the intestine ? To 
which class of food is intestinal digestion, however, devoted? What 
is the length and surface of the intestinal tube ? What two systems 
of apparatus does it contain ? 



INTESTINAL DIGESTIVE FLUIDS. 53 

the discharge of two totally distinct functions, digestion 
and absorption. It is, perhaps, this double duty which 
demands so extensive a surface, and not the necessities 
of heat-making digestion alone. 

Like the stomach, this tube consists of three coats — 
a serous, a muscular, and a mucous. The latter is gath- 
ered up in its interior into numberless projecting folds 
— the valvula? conniventes. These serve to increase the 
surface to which the food is exposed, and perhaps af- 
ford a mechanical obstacle to its passing too quickly 
forward. They tend also to break the continuous mo- 
tion, and bring the interior parts of the chyme to the 
surface. The onward movement is of course due to the 
pressure exerted conjointly by the straight and circular 
tibres of the muscular coat. Anatomists divide the tube 
into three portions — the duodenum, jejunum, and ileum. 

Soon after the chyme has escaped through the pyloric 
valve into the duodenum, it comes under the influence 
of the bile and pancreatic juices, sometimes discharged 
upon it at a common point, and sometimes at a little 
distance apart. Almost simultaneously it is submitted 
to the mechanical action of the valvulse conniventes. 
As the intestine is distended, these project with a cer- 
tain degree of turgidity, and accomplish their mechan- 
ical object. 

But, besides the pancreatic and biliary fluids, there 
are other juices thrown upon the passing chyme — the 
enteric juice, coming from B runner's glands, and a li- 
quid oozing from the follicles of Lieberkuhn; More- 
over, the organisms known as Peyer's glands are affect- 
ing the contents of the tube. Of each of these it is nec- 
y therefore to speak. 

1st The Pancreatic juice, secreted by the pancreas, 
an organ bearing a resemblance in its anatomical con- 
st met ion to the salivary glands, and hence usually re- 
garded a- one of that group. The juice itself is analo- 
saliva, being viscid, and in its reaction alkaline, 
it is Baid to contain no sulphoevanide nor any suspend- 
ed p articles. It acta opon starch even more energetio- 

What are the valvala- connivrntc- ? What is their 086? How 

do anatomists diride the intestinal fcnbe ? Mention the juices poured 
into ir. From what glands doe- the enteric juice come ? What are 
the properties of the pancreatic jni 



54 ENTERIC JUICE AND SECRETION OF LIEBERKUHN. 



Fig. 15. 



ally than saliva, transmuting it into sugar and lactic 
acid, and upon fats by forming them into an emulsion, 
so that they are readily absorbed. This has been found 
to take place in artificial experiments by submitting fat 
substances to the juice at a temperature of 100°. 

As would be inferred from the difference of emulsify- 
ing power between the saliva and this juice, its organic 
matter differs from ptyaline. It is estimated that the 
standard secretion of it is from five to seven ounces per 
diem. The action of the pancreatic juice appears to be 
limited to the upper half of the intestine. 

2d. The Enteric juice is secreted by the organs known 
as Brunner's glands, the structure of which has a cer- 
tain analogy to the preceding, and, like it, these doubt- 
less belong to the salivary group. Brunner's glands 
occur chiefly in the upper part of the small intestine, 
presenting themselves in the submucous tissue thereof 
as little bodies, commonly compared by anatomists to 
hemp-seeds. They consist of lobules with ducts com- 
municating with a common outlet. Their secretion pos- 
sesses a more energetic 
power when mixed with 
bile and pancreatic juice, 
than the pancreatic juice 
alone, in producing fatty 
emulsions. 

In Fig. 15, a half dia- 
gram of one of these 
glands, a a represents the 
mucous surface of the in- 
testine, and b the lobula- 
ted gland, discharging its 
secretion through a common duct. 

3d. The secretion of the follicles of Lieberhulin, which, 
as shown in Fig. 16, are straight, narrow, caecal depres- 
sions of the mucous membrane, found all over the small 
intestine, and in a general manner analogous to the tu- 
bular follicles of the stomach. Their interior is lined 
with columnar epithelium, and in depth they are equal 
to the thickness of the mucous membrane, their closed 

How much of it is secreted per diem ? In what portion of the in- 
testine does it operate? Describe the structure of Brunner's glands, 
and that of the follicles of Lieberkuhn. 



^^m^^^m 




Diagram of Brunner's glands. 



PEYER S BODIES. 



55 




Diagram of follicles of Lieber- 
kuhn. 



ends being therefore in contact r; "- le - 

with the submucous tissue, and 
their mouths opening into the in- 
testine. In a stale of health they 
contain a clear mucus-like secre- 
tion. In inflammations of the part 
they are filled with a more opaque, 
whitish liquid. From their resem- 
blance to the follicles of the stom- 
ach which secrete pepsin, it may 
be presumed that they possess a 
somewhat similar function ; but in 
the stomach, the resulting secre- 
tion is brought in relation with 
acids ; in the intestine, with alka- 
line bodies; and hence the physiological action may dif- 
fer in the two positions, though the structure and pri- 
mary function may be the same. 

4th. Th< Ion of Payer's glands. These may be 

ibed as circular spots, of a whitish color, and about 
the tenth of an inch in diameter, constituting glandular 
patches full of cell germs, but without any excretory 
duct opening into the intestine. It is supposed that 
they discharge their contents by rupturing at a cer- 
tain stage of their development. The solitary and ag- 
minate glands appear to belong to the same physiolog- 
ical group. 

The two conditions of 
the Peyerian glands are 
shown in Fi<j. 17, the 
right one being empty, 
ontents having been 
discharged, the left one 
still full. J>y some it is 
denied that these b< 
are connected with intes- 
tinal digestion. The I 
that vascular loops pass 



Fig. IT. 







into their grannlar contents, and that the lacteals hear a 

definite relation t<> them, seem to indicate that they are 
rath- :' the absorbent mechanism. 



1 1 - - ..ujcJs. 



To v. in; system <!«> they probably be- 



56 THE BILE. DIGESTION OF STARCH. 

5th. The bile. Of this it is not now necessary to 
give a detailed description, since that will occur more 
appropriately in treating of the functions of the liver. 
For the present purpose, it is sufficient to state that bile 
is a greenish-yellow liquid, of bitter taste and alkaline 
reaction. 

It does not appear to exert any agency in effecting 
the digestion of either nitrogenized or amylaceous bod- 
ies. The period of its maximum production, which is 
13 or 14 hours after a meal, does not coincide with the 
period of most energetic digestion. 

With these statements of the nature of the various 
juices passing into the small intestine, we may proceed 
to investigate the phenomena of the digestion carried 
on in that tube. 

Of respiratory elements, starch is one of the most im- 
portant, occurring as it does in abundance in vegetable 
food. It can not be made use of in the system without 
first being transmuted into dextrine, sugar, and eventu- 
ally lactic acid, these changes being greatly expedited 
if it has been previously prepared by boiling in water, 
or other equivalent operations of cooking. The saliva 
commences the action, which in man is even prolonged 
in the stomach, and in the herbivora still more decisive- 
ly in the paunch, in birds in the crop. On gaining the 
stomach, the farther transmutation of the starch is ar- 
rested by the gastric juice, but after reaching the duo- 
denum it is resumed with greater energy than ever, un- 
der the influence of the pancreatic juice. Reaching the 
ileum, the intestinal juice continues the action, though 
with less vigor. In this passage to the large intestine, 
the starch is gradually assuming the condition of dex- 
trine and sugar, the former substance passing into the 
latter with such facility that it can only be recognized 
transiently. Doubtless the sugar thus arising is in great 
part directly absorbed, though some, before the caecum 
is reached, is transmuted into lactic acid, and other por- 
tions, after passing through the ileo-caecal valve, into 
butyric acid. 

What is the bile ? Is it concerned in digestion ? What is the 
time of its maximum flow ? What change must starch undergo be- 
fore absorption ? What juices accomplish that change ? What be- 
comes of the sugar arising ? 



DIGESTION OF SUGAK. — LACTIC ACID. 57 

From what has been observed respecting starch, it 
may be interred how important sugar is, since through 
the condition of sugar alone is starch available for the 
uses ot* the system. It is to be recollected, however, 
that sugar itself is only an intermediate or transitory 
stage, a consideration which explains the circumstance 
that it does not occur even in the portal blood to such 
an extent as might be expected, nor yet in the chyle. 
Some have been led to infer from these facts that this 
substance, like gum, is in reality only very tardily ab- 
sorbed, an opinion they suppose to be strengthened by 
the circumstance that glucose or any other kind of sug- 
ar, introduced into the jugular vein, runs through the 
course of the circulation, and is secreted unchanged by 
the kidneys. But it is to be remembered that portal 
blood is very different from the proper systemic blood, 
and that there are many changes, beyond all question, 
taking place with rapidity in the former, but which do 
not take place in the latter. 

ajar, whether it has been received as an ingredient 
of the food, or arisen from the metamorphosis of starch, 
18, as we have said, only a temporary form, passing 
quickly onward to the state of lactic acid. To this we 
must impute the acid reaction observed throughout the 
length of the small intestine, and which can not be at- 
tributed to the gastric juice, a reaction occurring in spite 
of the alkalinity of the bile and pancreatic secretion. 
This pushing forward to the state of lactic acid is very 
generally imputed to the intestinal juice, which greatly 
re-enforces the power of the saliva and pancreatic fluid. 

On examining the process of the production of lactic 
ar-id during the souring of milk, we observe that every 
thing depends on the change occurring in the nitrogen- 
I principle, the casein. This, under the circumstan- 
n an incipient oxidation, and compels the 
nr atom so to divide as to give rise to the produc- 
tion of lactic acid. Thil the moment the casein 

\ the moment the ca- 

Whal fad has I sugar and gum arc tard- 

Dji [ntowhaf it change? Whal juice occasions 

? Descri (action and properties of lactic acicL Whal 

the circumstance! under which lactic acid arises in milk? In 

that change, what is the influence of the casein ? 

c _ 



58 DIGESTION OF FAT. 

sein is permitted to reoxidize. The destruction taking 
place in the casein is propagated to the sugar, the phys- 
ical peculiarity being that each atom of sugar is merely 
divided, fissured, or split, and gives rise to the produc- 
tion of two atoms of lactic acid, and no other substance. 
The whole process is therefore essentially one of subdi- 
vision, a conclusion to be carefully borne in mind in ap- 
plying these experimental principles to the physiologi- 
cal function of digestion. So far as the result is con- 
cerned, the two cases are the same. 

We can not here fail to remark how the process of 
comminuting the food is carried forward to such an ex- 
tent that the absorbent vessels are able to take it up. 
The action first begins, as has been shown in detail, by 
cutting and crushing implements, the teeth, and when 
these have carried the subdivision as far as mechanical 
means can, it is continued by chemical agents. Upon 
these principles, the pancreatic juice divides starch into 
lactic acid in duodenal digestion — a product which, 
without difficulty, finds its way at once into the system. 

Besides starch and sugar, there is another group of 
bodies belonging to the class of calorifacient food. In 
the case of carnivorous animals it seems to be exclusive- 
ly employed. The fats and oils constitute this group. 

The action of the pancreatic and enteric juices upon 
these bodies is to bring them into the condition of an 
emulsion, as may be easily proved experimentally. That 
this occurs in the intestine appears from the fact that 
if the pancreatic duct be tied, no emulsion forms, and 
the chyle in the lacteals is limpid instead of being milky. 
In the rabbit this duct opens much lower in the intes- 
tine than the biliary, and it is observed that it is only 
after the food has passed that point that it becomes 
emulsioned. The place for pancreatic digestion seems 
to be very constant in tribes that are far apart in hab- 
its of life. Thus, in fishes, the pancreas consists of a 
coronet of csecal tubes, surrounding the pyloric extrem- 
ity of the intestine, each opening into that organ by a 
separate mouth. 

What is the true nature of the change of sugar into lactic acid ? 
What is the general nature of digestive operations ? What is the 
calorifacient food employed by carnivorous animals ? What action 
do the pancreatic and enteric juices exert on fats ? 



ILLUSTRATION FROM THE MAKING OF AVINE. 50 

The fata reach the duodenum without undergoing 
any change. There, under the influence of the pancre- 
atic juice, they become subdivided into extremely mi- 
nute portions, which, absorbed by the lacteals, give to 
the chyle its characteristic aspect. Beyond this condi- 
tion of subdivision no other change is thus far impressed, 
the fat of the lacteals being absolutely the same as that 
of the chyme. To the introduction of fat into the lac- 
teals, the presence of bile seems to be necessary, or, if 
not absolutely necessary, absorption is greatly facilita- 
ted by it. 

Directing our attention now more particularly to the 
phenomena displayed by a changing nitrogenized prin- 
ciple, the following illustrations will serve to show that 
there is nothing mysterious in its operation. Out of 
many cases that might be selected, those now to be of- 
fered are more particularly interesting, since they refer 
to substances extensively used in the diet of man. 

First, <>f wine. A grape, if perfectly sound, will keep 
for a considerable length of time without undergoing 
any change; but if a puncture be made in it to give the 
air access, it rapidly deteriorates. The precise change 
taking place is perhaps better understood by observa- 
tions on the expressed juice of this fruit. If grapes be 
pressed beneath the surface of quicksilver, and the juice 
be collected in an inverted jar, without ever coming in 
contact with the atmospheric air, it may be kept for a 
long time without any apparent change; but if a small 
quantity of air, or only a single bubble of oxygen is per- 
mitted to enter the jar, and the temperature is that of 
a summer's day, a commotion or fermentation at once 
. carbonic acid escapes, alcohol arises in the liquid, 
and the BUgar which was in the grape-juice disappears. 
But the quantity of sugar thus capable of being de- 
str< limited, and a point is eventually reached at 

which no more Bagar can be decomposed, and no more 
carbonic acid pel free. 

ill- grape contains a nitrogenized princi- 

reaching the duodenum? 

ribe what occurs to them there:? What condition is necessary 

for the activity of changing nitrogenized bodies? Illustrate their 

action from ti. . is it that, in that Operation, 

carbonic acid and water arise ? 



60 ILLUSTRATION FROM THE MAKING OF BREAD. 

pie resembling albumen. It is this which is in reality 
the active body. So long as oxygen is excluded, this 
nitrogenized substance remains unaltered, but the mo- 
ment the air finds access a change begins. The sugar 
present in the juice becomes involved in the movement 
going on ; this is propagated by degrees to all its atoms, 
dividing each into two well-known and well-marked 
bodies. The period at which no farther change takes 
place in portions of sugar which may have been pur- 
posely added is when the nitrogenized principle has dis- 
appeared. 

Carbonic acid and alcohol are the two substances aris- 
ing in this decomposition. Their mode of origin is ob- 
vious when it is understood that one atom of sugar can 
be so divided as to yield four of carbonic acid and two 
of alcohol. 

Second, of bread. If, in the preceding case, a trans- 
muting nitrogenized body breaks the sugar atom so 
that alcohol is one of the products, and upon this prin- 
ciple all wines and intoxicating liquors are made, the in- 
stance now presented is of far more interest to the well- 
being of man. The use of wine undoubtedly adds not 
only to social enjoyment, but sometimes conduces to 
health — a benefit, alas ! often attended with a thousand 
ills. Not so with bread, emphatically and truly de- 
scribed as the staff of life. 

The making of wine and of leavened bread are two 
of the oldest chemical processes. Their origin is lost 
in a remote antiquity, and so universally are their ben- 
efits acknowledged that their use is diffused all over the 
world. 

Experience proves that the best bread is made from 
fine wheaten flour, mixed into a paste with a due pro- 
portion of water. A certain quantity of a nitrogenized 
substance undergoing incipient oxidation, termed yeast, 
is added, and the whole submitted to a gentle tempera- 
ture. All flour contains a small quantity of sugar ; on 
this the yeast immediately acts, dividing it, as in the 
former case, into carbonic acid and alcohol. If enough 
sugar is not present, more under the circumstances is 
formed from starch. The acid gas, as it is set free, can 

Illustrate it from the making of bread. What is the use of the 
yeast in that operation? 



ILLUSTRATION FROM THE MAKING OF BREAD. 61 

not extricate itself from the surrounding dough, but ex- 
pands into a thousand little vesicles or bubbles, which 
give that peculiar porosity for which this kind of bread 
is so highly prized. At this period, before baking, the 
other substance arising from the destruction of the sug- 
ar — the alcohol — is contained in the dough, and is ex- 
pelled therefrom along with the excess of water by the 
high temperature of the oven, which also, by increasing 
the expansion of the included gas, adds to the porosity 
of the bread. 

On some occasions, instead of using yeast, a piece of 
leaven, that is, dough in a state of incipient putrefac- 
tion, is employed. The mode of action is, however, the 
same. The use of this material well illustrates the pro- 
gressive nature of these changes, and how the action 
gradually passes from point to point of the entire mass. 
*• .V little leaven leaveneth the whole lump." 

In the cases here presented the action is one of sub- 
division. A complex atom has its constitution broken 
up, and is separated into distinct parts. When such a 
change is once commenced in a mass, there is a liability 
for the whole to become involved, just as, when we ig- 
nite one point in a pile of combustibles, the fire spreads 
throughout; or as, when on one part of a piece of fresh 
meat a small portion in a putrescent state is laid, the 
corruption, with measured rapidity, proceeds from part 
to part, until the whole is decayed. One after another, 
the particles submit in succession. 

Over all these subdividing actions heat exerts the 
most extraordinary influence, so that for a given effect 
to be produced it is absolutely necessary that a given 
temperature should be maintained. Thus, if we take 
the saccharine juice of almost any kind of fruit, and 
cause it to be acted on by a changing nitrogenized body, 
it will yield, as just stated, alcohol and carbonic acid so 
long as the temperature ranges about 75°; but, every 
thing remaining the same, if the temperature be raised 
or 120 . neither alcohol nor carbonic acid is 
formed, bat in their stead other products arise, such as 

What tf the alcohol of the dough ? Etow is it that leaven 

? What i- the chemical nature of these ferment actions ? What 
influence does heat rthem? Compare the fermentation of 

fruit juices and milk at different temperatures. 





62 EFFECTS OF TEMPERATURE ON FERMENTS. 

lactic acid, gum, and manna. Though, therefore, decom- 
position will go on throughout all this range of temper- 
ature, the products will vary very much, alcoho.l being 
formed at a low, and lactic acid at a high degree. 

Again, the decomposition of milk furnishes a very in- 
structive instance. When the temperature ranges from 
50° to 75°, the liquid turns sour, owing to the forma- 
tion of lactic acid ; but if the temperature is over 90°, 
the products are different, for now a true vinous fer- 
mentation sets in, alcohol and carbonic acid appearing. 
It is on this principle that the Tartars make an intoxi- 
cating liquid from mare's milk. The fermentation of 
milk, therefore, yields lactic acid at a low, and alcohol 
at a high degree. 

On comparing these illustrations, the results stand in 
direct contrast, but both show the great influence a 
specific degree of heat exercises over such subdivisions ; 
and, as a consequence of this principle, which obtains 
equally in the physiological case, we recognize the ne- 
cessity of maintaining the cavity of the stomach and in- 
testine uniformly at a fixed temperature, otherwise there 
would cease to be any uniformity in the subdivision of 
the food, occasioned by the digestion there going on. 
These principles, moreover, lead to the explanation of 
the action of such stimulating substances as alcoholic 
liquids, pepper, etc., which at once determine a local el- 
evation of temperature ; they also explain the injurious 
effects ensuing from intemperate draughts of ice-cold 
water. 

A nitrogenized substance, in a state of change, can 
thus bring about a definite action on fibrin, coagulated 
albumen, or casein in the stomach, or on starch in the 
intestine, so long as a temperature of 100° is maintained, 
but in every known instance this transmuting power is 
totally destroyed by exposure to a very low or very 
high degree of heat. Large masses of animal matter — 
whole carcasses — may be preserved for many centuries 
unchanged if the temperature is kept down to 32°. A 
striking example of this occurs in the case of the extinct 
mastodons occasionally thrown on the shores of the 
Polar Sea from icebergs, in which they have been en- 
Why is it injudicious to use undue quantities of ice water ? 



CONTRAST OF GASTRIC AND INTESTINAL DIGESTION. 63 

tombed for many thousand years, their flesh remaining 
in a perfectly fresh and undeeayed state. And as re- 
spects a high temperature, an exposure to 212° totally 
destroys the power. On this principle, all kinds of meat 
or vegetable substances may be indefinitely preserved. 
If such are inclosed in metallic canisters, so as totally to 
exclude the atmospheric air, and exposed to a bath of 
boiling water, they may then be carried round the world 
without undergoing any change. 

From a review of all the preceding facts, we may 
conclude that a nitrogenized substance secreted by the 
follicles of the stomach, and undergoing incipient oxida- 
tion, acidulated with hydrochloric acid obtained by the 
decomposition of common salt, or with lactic acid pro- 
duced by a continuation of salivary digestion, has the 
power of dissolving coagulated albumen, and generally 
those articles of food belonging to the nitrogenized class; 
that this goes on in the stomach, it being the function 
of that organ to effect the digestion of this kind of food, 
and thereby contribute to the general nutrition of the 
cm. The muscular tissues are supplied from this 
source, and by the stomach their waste is repaired. 

Another and distinct digestion takes place in the in- 
testine, commencing immediately after the food gains 
the duodenum. It too is brought about by the action 
of a special liquid, a mixture of the pancreatic and in- 
testinal juices. The chemical reaction of this juice is 
alkaline ; in this respect it is therefore antagonistic to 
the gastric juice. This quality is due to the soda it 
contains, a substance derived co-ordinately with hydro- 
chloric acid from the decomposition of common salt. 
The digestion of starchy and saccharine bodies is thus 
effected by dividing them so as to produce lactic acid. 

This done, common salt is reproduced by the com- 
mingling of the gastric, biliary, and pancreatic products 
•ther. The salt is carried by the absorbents into the 
interior of the system, to be again decomposed. 

Moreover, the pancreatic and enteric jnices reduce 
and fatty bodies to the condition of an 

* h the effect of a high temperature on ferment? Compare 

ther the d . "in^ r (>n in the stomach and that 

in the intestine. How is it that the common salt is used? 



64 SALTS AND GASES OF THE INTESTINE. 

emulsion, or, if they be not present in the food, give or- 
igin to them. 

Of the salt substances usually occurring in the food, 
most disappear during their passage through the intes- 
tine ; more particularly is this the case with those of a 
very soluble kind. Of the sulphates and chlorides of the 
food, not even a trace may occur in the excrement. If 
these substances should not be required for the uses of 
the system, they are promptly removed by the kidneys, 
and in the same manner are disposed of any abnormal 
salt substances which may have been purposely admin- 
istered, as, for instance, iodide of potassium. 

The gaseous contents of the intestine originate in part 
from the air that has been introduced during the masti- 
cation of the food, in part from fermentative processes 
occurring after certain articles have been used which 
are only imperfectly digested, and in part from the en- 
dosmosis of gas from the blood through the walls of the 
intestinal capillaries. As compared with atmospheric 
air, though the composition must necessarily be very va- 
rious, the intestinal gas shows a great excess of carbonic 
acid and nitrogen, a diminution and sometimes even a 
total absence of oxygen, the presence of pure hydrogen, 
and of its carburets and sulphurets. The quantity of 
this latter gas is lpss than might be expected, and, as 
would be anticipated from the circumstances, the accu- 
mulation of gas is much more abundant in^the large than 
in the small intestine. 

As the digested mass passes onward, driven by the 
peristaltic motions through the convolutions of the in- 
testine, it becomes of a more solid consistency, the ab- 
sorbents gradually removing the liquid portions. By 
the time it has reached the caecum, the same effect which 
arose in the stomach from salivary digestion is repeated, 
for the traces of unabsorbed lactic acid cause nutritive 
digestion to be again feebly resumed, at° all events in 
herbivorous animals, if not in man, whose caecum is rudi- 
mentary, under the form of the appendix vermiformis. 
The effete remains are finally voided as faeces. Their 

From what have emulsions arisen ? What becomes of the salt 
substances as the food advances in the intestine? What are the 
chief intestinal gases? How have they originated? What occurs 
in the caecum of the herbivora? 



FORMATION OF FAECES. G5 

average, exclusive of water, is only about 1 1 ounce per 
day. These excrementitious remains, colored yellow by 
the coloring material of the bile, are partly derived from 
the residues of the food which have been unacted upon, 
and partly from the decay of the system itself. The 
microscope shows the remains of cell membranes, and 
the walls of vegetable vascular tissues, starch granules, 
and chlorophyll, the relics of cartilaginous and fibrous 
tissues, shreds of muscular fibre, fat-cells. From the di- 
gestive tract there have been derived mucus corpuscles, 
epithelial cells, and the coloring matter of the bile. Per- 
haps, too, much of the water which gives consistency to 
the ta?ces has been derived from the intestinal walls, for 
in quantity, under certain circumstances, it may exceed 
the amount that has been used as drink. In fact, nearly 
one fourth of the whole quantity of water in the body 
has exuded into the intestine and been reabsorbed. 

It is interesting thus to observe how the death of one 
part of the body ministers to the life of the rest ; for the 
nitrogenized and active principles of the juices secreted 
for the accomplishment of digestion are in a descending 
career, and are truly dying matter. The incipient stage 
of decay through which they are passing reacts on the 
food, and prepares it to replace those parts of the body 
which are ceasing from activity, and about to be re- 
moved. 

What becomes of the coloring material of the bile? Of what do 
the excrementitious residues consist ? Why is it that the intestinal 
water may increase so much ? What advantage is taken of the de- 
cay of material in the body ? 



66 ABSORPTION. 



CHAPTER V. 

OF ABSORPTION. 

Double Mechanism for Absorption. — TJie Lacteals and 
Veins. — Lacteal Absorption. — JDescriptio?i of a Vil- 
lus. — Introduction of Fat by the Villi. — The Chyle. — 
Causes of the Flow of Chyle. — Intermediate Changes 
on its Passage to the Blood. — Action of 'Beyer's Bod- 
ies. — Lymphatic Absorption. — Nature of Lymph. 
— Structure of the Lymphatic System. — Function of 
the Lymphatic System. — Production of Fibrin. — Cu- 
taneous Absorption. — Causes of the Floio of Lymph. 
— Apparent selecting Power of the Absorbents. 

The food, after digestion, though in the alimentary 
tract, is exterior to the animal system. Means have 
therefore to be resorted to for its introduction into the 
circulation, and its distribution to every part. This is 
accomplished by a double mechanism, one portion of 
which is adapted to the digestion occurring in the stom- 
ach, the other to that completed in the intestine. The 
veins profusely spread on the walls of the digestive cav- 
ity constitute the former apparatus, the lacteals the latter. 

THE LACTEALS AND MESENTERIC GLANDS, ABSORPTION 

OF FAT. 

The lacteals may be described as delicate tubes, con- 
veying materials absorbed from the intestine into the 
blood. Their mode of origin may be understood by 
considering them as projecting with a fine but blunt end 
from the inner coat of the intestine. The projection is 
covered over with smooth muscle cells and a plexus of 
blood-vessels, a continuation, as it were, of those of the 
mucous coat of the intestine itself; they are held to- 
gether by connective tissue, and over that is cast a cov- 
ering of cylindric epithelium. This construction con- 
stitutes what is called a villus, the shape of which is coni- 

What is the object of absorption ? Of what use are the veins in 
absorption? Of what use are the lacteals? Describe a lacteal. 
What is a villus ? 



DISTRIBUTION OF BLOOD-VESSELS TO THE VILLI. 67 




Fia.is. cal, or perhaps cyl- 

indrical. The villus 
may then be regard- 
ed as a process of mu- 
cous membrane. 

Fig. 18 represents 

the distribution of 

blood-vessels to the 

villi of the intestine 

of the monkey. The 

f figure was drawn by 

monkey. the camera lucida, aa 

being the arteries, Fig. 19. 

bb the veins. 

The form of the 
villi differs in differ- 
ent regions of the 
intestine. In the 
duodenum they are 
- elevated, lam- 
inated, and broader, 
.19. In the jeju- 
num, more project- 
ing or cvlindroid, 
Mg. 20, p. 68. In all 
cases, however, they 
are abundantly sup- 
plied with blood- 
vessels. Their epi- Distribution of blood-vessels on the villi of the 

thelial covering of duodenum, 

cylindroid cells is shown in the sectional diagram,^/;/. 
]>. 68 ; at b b is the origin of the lacteal arising 
•urely. 

amply are the villi supplied with blood-vessels, 
that if, after injection with coloring material, their eylin- 
dric epithelium be removed, they seem to be tinged all 
■r. Each cell of the epithelium appears to be filled 
with granular matter, and to have a well-marked nucleus. 
Some anatomist that that end of these cells near- 

Che cavity of the intestine is in reality open, and in 

What ifl tli" furm of the villi in tin; duodenum? What in the je- 
junum? What opinion has been entertained respecting their epi- 
il cells ? \ 




68 



STRUCTURE OF THE VILLI. 



Fig. 20. 




Distribution of blood-vessels on the villi of the je- 
junum. 

Fig. 21. 



this manner they ac- 
count for the ready- 
passage of oil glob- 
ules into them, and 
also for the appear- 
ance of solid foreign 
bodies. 

Though we have 
described the lac- 
teal as a vessel pro- 
jecting into the in- 
terior of the intes- 
tine, it is by some 
viewed rather as a 
mere excavation in 
the villus. The villi 
impart to the mu- 
cous membrane an 
aspect some- 
times likened to 
the pile of velvet. 
On an average, 
their number up- 
on a square inch 
is about 10,000. 
The entire num- 
ber of these or- 
ganisms, conse- 
quently, must 
amount to many 
millions. Atone 
time it was sup- 
posed that the lacteals open directly into the intestine 
— an opinion now universally abandoned. The action 
of each villus is doubtless more complicated than is gen- 
erally represented, for the organic fibre cells it contains 
give to it the power of executing rhythmic motions. 

When the operation of the lacteal vessels as absorb- 
ents was first detected, it was believed that all nutri- 
ment is introduced by their means. But there are many 

How many villi are there on a square inch ? Do they open di- 
rectly into the intestine? How is it that they can exert rhythmic 
motions ? What error was formerly entertained respecting them ? 




Conical villi in section, with cylindroid epithelium. 



INTRODUCTION OF FAT. 69 

animals wholly destitute of this system of tubes, for in- 
stance, the invertebrates. Even in many fishes the villi 
are absent. In such cases absorption must necessarily 
be conducted by the veins. Moreover, though there are 
no lacteals on the walls of the stomach, noiyindeed, on 
that part of the intestinal tube which is higher than the 
place of introduction of the biliary and pancreatic ducts, 
there are many substances freely absorbed from the gas- 
tric cavity when its pyloric orifice is tied. It has al- 
ready been mentioned that the stomach absorbs water 
with remarkable rapidity. The doctrine that the lac- 
teals are the exclusive organs of absorption must, there- 
fore, be abandoned, for it is plain that the venous sys- 
tem participates in the duty. 

The function of absorption has therefore to be exam- 
ined from two points of view. As there are two diges- 
tions, one producing a perfect solution, and the other an 
emulsioned, but not dissolved state of the food, so there 
are two absorbent systems, the lacteals and the veins. 
The lacteals introduce such substances as are not abso- 
lutely dissolved, the oils and fats. The veins appear to 
take up those substances only w T hich are completely dis- 
solved in water. 

That the lacteals are connected with respiratory di- 
gestion seems to be plainly indicated by the circum- 
stances of their occurrence. None of them are found 
upon the stomach, nor even on that part of the duode- 
num above the entrance of the hepatic and pancreatic 
ducts, but below that point they are scattered in pro- 
fusion all over the small intestine. The digestion of 
fatty bodies not taking place until the food has gained 
the duodenum, vessels for the absorption of the emul- 
sions to which that digestion gives rise are not required 
until after that point is passed. Correctly speaking, 
however, the lacteals are only lymphatics taking up oil 
presented to them. In view of the use the oils subserve 
in the animal economy, the lacteals are in reality an ap- 
pendix to the respiratory system. There can be no 
doubt that through their channel oils and fats, under 

How many form- of absorption are there? What do the lacteals 
and the veins respectirely absorb? How may it he shown that the 

lacteals are connected with respiratory digestion? Under what form 
do they transmit fat to the hlood ? 



70 INTRODUCTION OF FAT. 

the form of emulsions, are transmitted to the blood. 
The analysis of the chyle shows that it is always rich in 
fat ; and, indeed, it is supposed by some physiologists 
that the objects just described as cells, surrounding the 
origin of the lacteals, are nothing more than oil or fat 
globules accumulated there and waiting to be taken up, 
or that the disappearance and exuviation of the so-called 
cells is an optical deception, due to their walls becoming 
permeated with oil. 

The manner in which oil globules collect round the 
Fig. 22. villus I have remarked as 

being very strikingly dis- 
played in the case of the 
gray squirrel after feeding 
on fatty nuts. As shown 
in Fig, 22, the whole struc- 
ture looks as if it were dis- 
tended with oil globules, 
r ~i a a, in the midst of which 
t the origin of the lacteal, 
bbb, may be discerned. 

Half-diagram of villi of the gray squirrel Although it Can not be 

after feeding on nuts. admitted that the produc- 

tion and deliquescence of the cells of villi is a demon- 
strated fact, and that on this the action of the lacteals 
as absorbent vessels for the most part depends, the rapid 
evolution and disappearance of these cells is by no means 
a physiological impossibility. Botanists assert that, in 
a single night, the Bovista giganteum, a puff-ball, can 
develop from a mere point to such a size that it must 
contain fifty thousand millions of cells — a number that 
seems almost incredible. The development of cells in 
the villi of the intestinal tube, in countless crowds, may 
therefore be within the bounds of possibility. 

If this be the case, the cells thus coming rapidly into 
existence in the villi appropriate those articles of res- 
piratory food of imperfect solubility in water. To this 
class the oils belong. Each cell then, as it dies, yields 
up its contents to the lacteal tube. In the white fluid, 
the chyle, flowing along those tubes, are many pale or 
colorless corpuscles continually coming into existence. 
These seem to impress a change upon the chyle, and, to 

What may those objects round the lacteals be that look like cells ? 




MOTION OF THE CHYLE. 7l 

give a full opportunity for such action, that fluid is com- 
pelled to flow gradually through long and sinuous chan- 
nels, for the glands in the mesentery may be regarded 
as convoluted windings, or rather plexuses of tubes, hav- 
ing that particular form for the sake of closeness of pack- 
age. From the enveloping capsule of fibrous tissue of 
the glands thin sheets are projected, and so internetted 
as to divide the whole gland into many alveoli. These 
are rilled with a pulpy material supplied with delicate 
blood-vessels. Tho chyle either oozing through this ma- 
terial eventually escapes from the gland by the efferent 
vessels, or makes the passage in its own thin tube. In 
reptiles, in which there are no such glands, the lacteals 
are extended to a very great length. 

The manner in which the chyle passes through the 
mesenteric glands is therefore explained differently, ac- 
cording to the view taken of the structure of those or- 
gans. If they are considered as mere dilatations of the 
lacteal vessels, from the sides of which partition process- 
ire sunt off, the interspaces being filled with granular 
material, through which delicate blood-vessels pass, the 
chyle is to be considered as oozing through this granu- 
lar structure, and crossing directly in contact with it. 
But if we accept the doctrine that the chyle is conduct- 
ed through the gland in a plexus arising from the in- 
coming lacteal, the granular material being outside, then 
the influence of that material, in whatever it may con- 
. takes effect through the delicate walls of the plexus. 
The like remarks apply to the lymphatic glands. Phys- 
ically, however, the condition in both cases is the same; 
the incoming liquid is simultaneously exposed in the 
gland to the influence of the granular pulp and to arte- 
rial blood. 

Chyle, delivered into the lacteal tube, is propelled by 
the conjoint action of several different forces. The con- 
stant accumulation of liquid at the origin of the vessel 
produce- a pressure only relieved by motion through the 
tube, and at the mouth, where the lacteal empties into a 
veil or later all do, either directly or through 

the intervention of the thoracic duct, a suction forc< 

What i> tie structure of the mesenteric glands? What influence 

do they exert on the chyle? Describe the different forces that drive 
the chyle through the lac; 



72 



THE PRINCIPLE OP VENTURI. 



Fig. 23. 




Principle of Venturi. 



exerted on the contents of the lacteal by the passing cur- 
rent of the venous blood, upon the well-known hydraulic 
principle of Venturi, that if into a tube, a #, Fig. 23, 

through which a cur- 
rent of water is steadily 
flowing, another tube, 
c d, opens, its more dis- 
tant end being in com- 
munication with a reser- 
voir of water, e, through 
this tube a current will 
likewise be established, 
and the reservoir be 
emptied of its contents. 
The effect is still greater 
when the main current 
is flowing toward the 
wide end of a conical 
pipe. Moreover, the lac- 
teal tubes are elastic, 
and furnished with valves, opening to let the fluid pass 
toward the veins, but closing in the opposite way. This 
valvular mechanism renders available any pressure aris- 
ing either from the contractility of the vessels them- 
selves, or from those various muscular movements, res- 
piratory or voluntary, which affect the abdominal walls. 
The manner of introduction of the great lacteal trunk 
— the thoracic duct — at the angle of junction of the left 
subclavian and jugular veins, is also very felicitous, for 
the suction force of those large vessels is there conjoin- 
ed, and the effect is at a maximum. The control of the 
blood motion on the chyle motion is obvious from this, 
that as soon as the circulation stops the chyle stops, and 
this not so much from the engorgement of the venous 
trunks, rendering it difficult for the chyle to make its 
way into them, as from the cessation of that tractile 
force, which solicits the chyle to move into the blood. 

Fig. 24 represents the position and course of the tho- 
racic duct, and its manner of introduction of the chyle 
into the blood circulation. 



What is meant by the principle of Venturi ? How does it come 
into play on this occasion ? What is the thoracic duct ? 



INTRODUCTION OF FAT. 



73 



1, Arch of aorta ; 2, thorac- 7.7,7. u. 

ic aorta; 3, abdominal aorta; 
4, arteria iuuominata, dividing 
into right carotid and right 
subclavian arteries ; 5, left car- 
otid ; 6, left subclavian ; 7, su- 
perior cava, formed by the j mic- 
tion of, 8, the two venae inno- 
minata\ and these by the junc- 
tion, 9, of the internal jugular 
and subclavian on each side ; 

10, the greater vena azygos; 

11, the termination of the less- 
er in the greater vena azygos ; 

12, receptaculum chyli, several 
lymphatic trunks opening into 
it; 13, the thoracic duct, di- 
viding opposite the middle of 
the dorsal vertebra? into two 
branches, which soon reunite ; 
the course of the duct behind 
the arch of the aorta and left 
subclavian artery is shown by 
a dotted line; 14, the duct, 
making its turn' at the root of 
the neck, and receiving several 
lymphatic trunks previously to 
terminating in the posterior 
aspect of the junction of the 
internal jugular and subclavian 
vein ; 15, the termination of 
the trunk of the ductus lymphaticus dexter. 

A- to the manner in which digested fat finds its way 
into the lacteals, it seems to be as follows: In the inte- 
rior of the epithelial cells oil-drops are detected, while 
on the outer part the surface presents a pearly aspect, 
from Other portions of oil waiting to enter. By degn 
all the cells upon tin.- exterior of tin 1 villus exhibit the 
same appearance, the parti dually finding their 

way through the parenchyma of the villus, and so en- 
tering the lacteal tube In passing through interstices 

l) - /,_'{. In what manner do the fate And their way into 

the lacteal- ? 

1) 




The thoracic duct. 



74 CHANGES OF THE CHYLE. 

too minute to be seen even by optical aid, the oil par- 
ticles may be pressed out into long, thread-like forms, 
which, as soon as they escape into the free cavity of the 
lacteal, assume the spheroidal appearance by reason of 
their own cohesion, just as a blood-cell can pass through 
a vessel of a diameter far less than its own by lengthen- 
ing itself out into a linear shape, and reassuming its orig- 
inal figure as soon as it escapes from confinement and 
pressure. Though, therefore, the lacteals commence 
upon the intestinal walls as closed tubes, this, in reality, 
offers no obstacle to their absorbing power when their 
molecular porosity is considered. 

Perhaps this infiltration or intrusion of oily material 
is, to a considerable extent, aided by the presence of the 
bile. It is capable of demonstration that oil will rise 
much higher in a capillary glass tube, the inside of which 
has been coated over with bile, than in one which has 
not been so prepared. 

The liquid gathered into the lacteals from the intes- 
tine pursues its course to the veins, and ultimately en- 
ters them. The special changes impressed on it during 
this passage will now be explained. 

The constitution of the chyle varies with the physio- 
logical conditions of the system. After a period of fast- 
ing it is colorless, and presents the general appearance 
of lymph, hereafter to be described, but during diges- 
tion it is a whitish milky fluid, whence its name. This 
milkiness depends on the suspension of minute fat or oil 
globules in it. Their diameter is commonly stated at 
the 56 ^ 0Q of an inch. Of course, the composition of 
the chyle varies in different animals, and even in the 
same animal under different diets. 

How is it that the fat globules can pass through pores of less size 
than themselves ? What effect does the bile exercise ? Into what ves- 
sels does the chyle ultimately pass ? What variations in composition 
does the chyle exhibit ? 



CHANGES IN THE CHYLE. 



75 



Composition of Cliyle. 



f 


Horse. 


Man. 


Water 


935.00 

15.00 

.75 

35.00 

6.25 

8.00 


904.80 
9.20 

^ 70.80 

10.80 
4.40 


Fat 


Fibrin 

Albumen 

Extractive 


Salts 


1000.00 


1000.00 



With so many causes of variation, such a table as the 
preceding is only valuable as giving a general idea of 
the nature of the chyle. We learn from it that the pre- 
dominating solid constituents are fat and albumen. The 
percentage amount of the first of these in the sample of 
human chyle is very low, a fact due to the circumstance 
that the subject from which it was obtained — an exe- 
cuted criminal — had eaten but little for some time be- 
fore his death. In like manner, the chyle of horses kept 
without food has been observed to exhibit a diminution 
of its fat to such an extent as to be less than one tenth 
of the normal amount. It is to be remarked that the 
saline ingredients of the chyle closely represent those 
of the blood, both in constitution and amount. 

The composition of the chyle varies at different points 
on its passage to the veins, there being a gradual diminu- 
tion of the albumen and an increase of the fibrin. Aft- 
er the passage through the mesenteric glands it becomes 
capable of coagulation, and will separate into a serum 
and a clot. Examined near the villi, it may be regard- 
ed as an albuminous liquid, containing suspended glob- 
ules of fat of various sizes, down to the degree of mi- 
nuteness just specified. The nature of these globules is 
determined by the action of sulphuric ether, which readi- 
ly dissolves them. After passing through the mesen- 
teric glands, the percentage amount of albumen declines, 
and the fat globules diminish in number. Simultane- 
ously the special cells, chyle corpuscles, make their ap- 
pearance, and the liquid is now capable of coagulating, 
owing to the production of fibrin. These characters 
become more strikingly developed as the chyle advances 

What arc its characteristic ingredients? What change does it 
exhibit after passing the mesenteric ^land^? 



76 CHYLE CORPUSCLES. 

in the thoracic duct. The chyle corpuscles are event- 
ually developed into red blood-cells. 

It should be borne in mind, in all discussions respect- 
ing the composition of chyle in different parts of its 
course, that it must receive transuded matters from the 
blood, and that this must more particularly occur on 
its passage through the mesenteric glands. Owing to 
this, it is quite probable that, even though there should 
be an actual consumption of albumen in accomplishing 
the metamorphoses taking place, the apparent percent- 
age amount of that ingredient may increase by transu- 
dation from the blood. It appears to me quite proba- 
ble that the albuminous material in the lacteal, at its 
very origin in the villus, has been derived to quite as 
great an extent by transudation from the plexus of 
blood-vessels as by absorption from the digested food. 

Whatever may be the special manner by which the 
fats pass from the intestine into the lacteals, they have 
scarcely gained those vessels before they undergo a 
change. The quantity of free fat diminishes, and that 
of saponified fat increases ; this is probably accomplish- 
ed by soda obtained from the blood. 

As to the fibrin, it can scarcely be supposed that the 
imperfectly coagulable variety the chyle contains should 
have been derived by transudation through the vessels 
of the strongly contractile kind contained in the blood ; 
and, in view of all the circumstances of the case, it would 
appear that the explanation we shall offer of its direct 
origination from the chyle albumen by oxidation is cor- 
rect. 

The chyle corpuscles are readily distinguished from 
the blood-cells, not qnly by their white appearance, but 
also by their form. Tffey are spheroidal, and either 
homogeneous or granular. Those of the frog are seen 
in Fig, 25, at a a, sparsely scattered among the ellipti- 
cal blood-cells. The photograph from which the engrav- 
ing is taken exhibits nearly the average proportion of 
these bodies in that animal. 

In embryonic life, the first appearance of chyle cor- 

What do the chyle corpuscles eventually become? How do mat- 
ters transuding from the blood affect the chyle ? What change oc- 
curs to the fats in the lacteals ? Compare the chyle corpuscles and 
blood-cells. 



THE LYMPHATICS AND THEIR GLANDS. 




Chyle corpuscles with blood-cells, magnified 250 
diameters. 



puscles commonly 
coincides with a, 
change in the ar- 
rangement of the 
respiratory mechan- 
ism, as the closing 
of the branchial fis- 
sures, indicating a 
connection between 
their production and 
the activity of inter- 
stitial oxidation. 

The bodies known 
as Peyer's glands 
are to be regarded 
as belonging to the 
absorbent rather 
than the digestive 
apparatus. In structure they are analogous to the lym- 
phatic glands, consisting of a capsule containing granu- 
lar material, in which loops of capillary blood-vessels 
are laid. From these proceed many lacteal vessels, as 
may be very plainly observed during digestion. Their 
functions would therefore seem to be the submitting of 
the chyle to the simultaneous influence of the blood 
brought by the arterial capillaries, and the pulpy mate- 
rial or granular plasma they contain. They are, in real- 
ity, intestinal mesenteric glands. 

THE LYMPHATICS AND THEIR GLANDS. 

It is not possible clearly to understand the functions 
of the lacteals without a description of the structure and 
functions of the lymphatics, for these vessels conspire in 
their action. 

Anatomical, chemical, and physiological considerations 
lead us to conclude that the formation of the LYMPHAT- 
v-ti:m r> closely allied to that of the LACTEAL. The 
two elas-es of vessels make their appearance together in 
fishes; the lymphatics originate in a network of delicate 
tubes, but are disseminated through all the soft tissues 

When do the chyle corpuscles first appear? What is the struc- 
ture and probable use of layer's bodies? How arc the lymphatic 
and lacteal systems allied ? 



78 PKOPEKTIES OF LYMPH. 

except the nervous, and are found especially in the skin. 
The fine initial tubes gradually coalesce, producing those 
that are of a larger diameter, and these pass through 
glands, which might indeed be regarded as mere plex- 
uses, and eventually empty into the veins. 

A few minutes after it has been drawn, the lymph co- 
agulates into a colorless clot, and then exhibits contrac- 
tion. Compared with blood in like circumstances, the 
clot of lymph is small in relation to the serous portion. 
In other respects there is a general resemblance between 
lymph and blood free from its red cells, the fibrin and 
the albumen being apparently the same in the two cases. 
The saline constituents are not only the same, but bear 
the same ratio to one another in the two fluids. Their 
absolute percentage amount differs, because the lymph 
contains a larger proportion of water than the blood. 

Lymph arising, as we shall find, by transudation from 
the capillaries, must obviously vary in different parts, 
those parts taking from the blood the materials they re- 
quire for their nutrition, and yielding to it the products 
that have arisen during their waste. Whatever in this 
manner changes the composition of the blood, must also 
occasion a change in the transuded liquid. Not only 
must the material thus oozing from the capillaries vary 
in different regions, because of variations in the mechan- 
ical constitution of those vessels, but it must also change 
even in the same locality, through temporary accidents, 
such as changes in the velocity with which the blood is 
flowing. An attempt has been made to show that the 
transudation will be richest in albumen as the blood cur- 
rent in the capillaries is slower. 

When the contents of the lymphatic vessels are sub- 
mitted to analysis, and compared with the chyle, a strik- 
ing difference is apparent. The chyle contains, as has 
been already stated, large but variable proportions of 
fat or oil in an extremely subdivided state, from which 
the lymph is free. The leading solid constituent of the 
lymph is albumen, and this indicates the use of the sys- 
tem. 

Describe the properties of lymph. What is the relation of its sa- 
line ingredients to those of the blood ? What is the origin of lymph ? 



THE LYMPHATIC SYSTEM. 

Composition of Lymph. 



79 





Horse. 


Man. 


Water 


950.00 
.09 

^ 39.11 

4.88 
5.92 


961.00 

2.50 

27.50 

6.90 

2.10 


Fat 


Fibrin 


Albumen 


Kxtractive 


Salts 




1000.00 


1000.00 



The constitution of chyle after a period of fasting is 
the same as that of the lymph. The presence of chyle 
in the lacteals is therefore not a constant but a periodi- 
cal phenomenon. The analogy of composition between 
lymph and chyle shows clearly that the albumen of the 
latter is rather derived from the blood capillaries than 
from the digested food. 

There can be no doubt that the office of the lymphat- 
ics is to collect the albuminous matters which have ev- 
ery where transuded from the blood-vessels, or been set 
free by changes going on in the soft parts. Such mat- 
ters, though they may be regarded as being in one sense 
dead, are yet as applicable for the farther support of the 
mechanism as are the albuminoid bodies introduced as 
food, and said to be taken up by the lacteals. Lymph 
is really nothing but a diluted serum. A mechanism is 
therefore resorted to to turn this collected albumen into 
fibrin, and thus arises a lymphatic gland — a contrivance 
tending greatly to compactness. This structure is the 
counterpart of the mesenteric or lacteal gland. It may 
be described as originating from the coalescence of two 
or three lymph vessels, which, casting off their external 
coat as they enter the gland, anastomose with one an- 
other in various ways, so as to form plexuses and con- 
volutions. The capsule of the gland, strengthened by 
the coat it has received from the entering vessels, sends 
forth partition-like processes, dipping down into the 
grayish pulpy material that fills the interstices. On 
their emergence from the gland the vessels recover from 
it their external coat, rm<l. daring their passage through 

What is its composition? What is the relation between fasting 
chyle and lymph? How LB it that the presence of chyle in the lac- 
teals is periodic? What is the office of the lymphatic system? De- 
scribe the structure of the lymphatic glands. 



80 PKODUCTION OF FIBRIN. 

it in their naked state, blood-vessels are distributed upon 
them. The object of the arrangement seems to be to 
submit the liquid contained in the lymph vessel to the 
action of the pulpy material of the gland and arterial 
blood under the most favorable circumstances, the thin- 
ness of the wall and the convolved plexus being well 
adapted to that end. 

The absorbent vessels, whether lacteals or lymphatics, 
have therefore a common duty of changing albuminose 
or albumen into fibrin, and thereby of compensating for 
the constant waste of that substance going on in the 
wear and tear of the muscular system. We can not es- 
timate the hourly consumption at less than 6* grains. 
Such a waste must demand an equivalent compensation, 
if the animal mechanism is to be kept up unimpaired, 
and every care is therefore taken to omit no means of 
husbanding the necessary materials. The action of the 
lymphatics illustrates this principle significantly. Pass- 
ing through all the soft solids where exudation of albu- 
men from the blood-vessels can take place, they collect 
the materials that would otherwise go to waste, and add 
thereto many of the products arising from the disinte- 
gration and decay of the soft parts themselves. Receiv- 
ing all these, they transmit them through their windings 
in the glands, and thus submit them to the action of the 
innumerable cells there coming into existence. As in 
the egg of a bird, the albumen slowly disappears, and 
muscular tissues of the young chicken arise, so here the 
serous portion disappears, and fibrin comes in its stead, 
and this is hurried forward to the torrent of the circula- 
tion, and thrown into the blood-vessels, to be by them 
distributed to all parts of the mechanism, wherever the 
muscular tissues are in want of repair. 

But, besides this function of the elaboration of fibrin, 
there can be no question that the lymphatics have other 
incidental uses. Many facts are known, proving that 
those of the skin exert a powerful agency in absorbing 
liquid material. Thus a person who has abstained from 
water will, after he has immersed his body in a bath, not 

From what do the absorbent vessels produce fibrin ? How much 
is its hourly waste ? What analogy does the egg of a bird present to 
these results ? How is it known that substances may be absorbed by 
the lymphatics of the skin ? 



CAUSE OF TIIE FLOW OF LYMPH. 81 

only find his weight increased, but the sensation of thirst 
abated. Instances of the kind are on record where sail- 
ors, in open boats without fresh water, have assuaged 
the torments of thirst by immersing their bodies in the 
sea. Nay, it is even asserted that in certain conditions 
water may thus be obtained from the atmospheric air, 
and in all such cases every thing points out that the 
lymphatic vessels are the avenues through which the 
liquid is introduced. 

In what manner does the lymph move? In reptiles 
are found what are termed lymphatic hearts ; these are' 
merely dilated portions of a tube exhibiting pulsation. 
In the frog, two pairs may be discovered, one behind 
the hip*joint, and situated so superficially that the mo- 
tions can be plainly seen ; the other is at the anterior 
part of the chest. The pulsating movements of these 
organs, of course, impel the liquid acted on in the direc- 
tion determined by the valves with which the vessels 
are so profusely supplied — that is, to the general circula- 
tion, and the lymph finally enters the blood-vessels. 

But in the higher tribes these organs of impulsion are 
absent, and the circulation through the vessels is determ- 
ined by the agencies mentioned in the case of the lac- 
teals. 1st. By the constant accumulation of liquid at the 
origin of the tube ; 2d. By every muscular movement, 
either voluntary or involuntary, producing a compres- 
sion of the tube, the valves all opening one way, and 
therefore causing the included liquid to pass in one di- 
rection only ; 3d. By the exhaustive action at the mouth 
of the lymphatic, arising from the passage of the blood. 
It ought, perhaps, to be prominently pointed out, as be- 
longing to the second of these causes, that the pulsation 
of the arterial trunks adjacent to any lymphatic brings 
the power of the heart itself into operation in an indi- 
rect way. 

Though the absorbents receive many different bodies 
and transmit them to the veins, the action does not take 
place in an indiscriminate manner. Certain substances, 
such as the fats and albumen, find a ready entrance, but 
admission to others is wholly denied. Thus it has long 

I describe the ich give rise to motion in the lymph. What 

are lymphatic hearts? What effect do the arterial trunks exert? 
What i> mr-ant by the selecting power of the absorbents? 

]) 2 



82 SELECTING POWER OF THE ABSORBENTS. 

been known that if coloring matter be introduced into 
the intestine, it by no means follows that the chyle will 
be tinged. If an animal be compelled to take litmus 
water, the chyle will still be found colorless or white. 
On such facts was founded the old doctrine that these 
organs possess a low species of intelligence, distinguish- 
ing among different substances, permitting some to en- 
ter them, and refusing a passage to others. Many years 
ago I showed that these fanciful cases are capable of a 
simple physical explanation. Thus I found that if blue 
litmus water were tied up in a bladder or a piece of per- 
itoneum, and sunk in a vessel of alcohol, though the wa- 
ter would rapidly infiltrate into the alcohol, the coloring 
matter would be stopped just as it is in the intestine. 
But, in reality, there is no need of such experiments to 
satisfy us of the fictitious nature of this selecting power. 
If we fill a lamp half full of oil and half of water, and 
immerse in it a wick long enough to dip into both, if the 
wick be previously soaked in oil, it will withdraw from 
the lamp oil alone, and continue to do so until the lamp 
ceases to burn ; but if it be first soaked in water, it will 
wholly refuse to take the oil, and remove the water alone, 
until all has escaped by evaporation. But did ever any 
one impute to the wick of a lamp a power of intellectual- 
ity, no matter how obscure, or suppose that there is any 
thing mysterious in such a selecting operation ? A per- 
petual reference of the most common facts to mysterious 
agencies has been the great barrier to the advance of 
medical science. This system was introduced by the al- 
chemists and quacks of the Middle Ages, and even now 
it will take many books and many years before physiol- 
ogy can be rescued from such visionary theories. 

How may the selecting power of the absorbents be illustrated ? 



ABSORPTION BY THE BLOOD-VESSELS. 83 



CHAPTER VI. 

ABSORPTION BY THE BLOOD-VESSELS. 

Proof of Absorption by the Blood Capillaries. — Oc- 
curs as a Physical Necessity. — Nature of Capillary 
Attraction. — Its Phenomena in the Pise and Depres- 
sion of Liquids. — Conditions for producing a Flow 
in a Capillary Tube. — Passage of Liquids through 
minute Pores. — Endosmosis and Exosmosis. — Tliey 
depend on Capillary Attraction. — Force against 
which these Movements may take place. — Illustra- 
tions of selecting Power. 

Titat the blood-vessels of the stomach and intestinal 
tube participate in the function of absorption is demon- 
strated by many different facts. Medicaments placed in 
the stomach after its pyloric orifice has been tied will 
produce their specific effect almost as rapidly as under 
natural circumstances ; and, since there are no proper 
lacteals upon that organ, and its lymphatics seem to be 
inadequate, the absorption of these agents can have 
taken place through the blood-vessels only. 

This conclusion is substantiated by an examination 
of the blood of the gastric and mesenteric veins. It va- 
ries with the stage of digestion and the nature of the 
food. At first there is a general lowering of the per- 
centage amount of the solid ingredients, this being evi- 
dently the result of the absorption of water. At a more 
advanced period, the relative proportion of albumen, or 
rather of albuminose, rises, and along with it the extract- 
ive, gelatine, and sugar increase. As with the chyle in 
the lacteals, so with the blood in the mesenteric veins, 
coagulation takes place imperfectly, or not at all. The 
myenteric blood of a fasting animal does not differ from 
the ordinary venous blood. 

TTow may it be proved that the blood-vessels of the stomach ab- 
.' What changes take place in the blood of the gastric and mes- 
enteric veins during digestion? 



84 PHYSICAL NECESSITY OF VASCULAR ABSORPTION. 

The position of the blood-vessels, both on the mucous 
surface of the stomach, and particularly on the villi of 
the intestine, is favorable to the discharge of this func- 
tion. The term venous absorption, employed to express 
it, is perhaps somewhat incorrect, since there is no rea- 
son that a venous capillary should have any advantage 
over an arterial one in this respect. 

In fact, if there were not these physiological consid- 
erations, we should have to admit absorption by the 
blood-vessels as a matter of physical necessity ; for, un- 
der the circumstances of their situation, they must take 
up soluble matters presented to them. Through the 
pores of their delicate structure substances in the liquid 
state will pass to mingle with the blood. 

Though we have treated of respiratory or lacteal ab- 
sorption as specifically distinct from absorption by the 
blood-vessels, the circumstances here alluded to evident- 
ly point out that the resulting action of the villi of the 
intestines is of a mixed kind ; for, though the epithelial 
cells and the commencing pouch of the lacteal may exert 
a definite influence, the network of bood-vessels which 
lies immediately beneath the epithelium must be engaged 
in precisely the same manner as the network of blood- 
vessels between the gastric follicles. The permeation of 
the walls of these tubes by substances in a state of solu- 
tion is dependent, as we are now to see, upon a purely 
physical principle, just as applicable in the one case as it 
is in the other. 

In absorption, as in respiration, hereafter to be de- 
scribed, there is a physical principle in operation neces- 
sary to be understood. I shall proceed to explain it on 
this occasion as far as is needful for the present purpose, 
and complete the description in the chapter on the func- 
tion of respiration. The peculiar views here set forth, 
so far as they differ from those ordinarily expressed, I 
believe to be warranted by my own experiments else- 
where published. 

The absorbent action of the blood-vessels depends on 
the force known among physical writers as capillary 
attraction. Its nature may be illustrated as follows : 

Why is the term venous absorption incorrect ? "V^hy is venous ab- 
sorption a physical necessity ? What is the reason that the action 
of the villi is of a mixed kind ? 



CAPILLARY ELEVATIONS AND DEPKESSIOXS. 85 



If a piece of glass be laid on the surface of quicksilver, 
it is so powerfully attracted thereto as to require the ex- 
ertion of considerable force to lift it off. Natural phi- 
losophers generally regard this as a force sui generis, 
and speak of it under the title of capillary attraction. I 
believe it is nothing but an ordinary electrical phenom- 
enon, since, if the glass be examined, it will be found to 
be in a positively electrified state, and the quicksilver 
negative, and under the general law of electricity, known 
as that of Dufav, attraction must be the result. 

If the glass be laid upon the surface of water, there is 
an attraction as before. On lifting it, 
however, there is no electrical manifes- 
tation. The reason of this is plain. On 
examining this glass, it will be found 
that no true separation of it from the 
water has taken place. A film of wa- 
ter is still attached to it, or, in other 
words, it is wetted. 

If a slender glass tube, b, Fig. 26, be 
dipped into a liquid, a a, which can not 



Fig. *G. 






wet it. 



as, for ex- 




Depression of a non- 
wetting liquid. 



ample, quicksil- 
ver, the liquid is 
depressed as at 
c, and does not 
rise to its proper 

hydrostatic level, or, perhaps, alto- 
gether refuses to enter the tube. 

If a slender glass tube, b,Fig. 27, 
be dipped into a liquid, a a, which 
can wet it, as, for example, water, 
the liquid at once rises in the tube, 
as at C, to a height greater in pro- 
portion as the diameter of the tubo 
is less. This phenomenon has given 

the designation capilhir;/ (ittrni-titm, because it is best 

seen in tubes as fine as a hair (capillns). 

W if there be a tube of such a diameter that it can 

thus lift water ten inches, and it be broken off so as to 

Define capillary attraction. Why u it ded as an elec- 

trical phenomenon ? Explain the circumstance* under which liquids 
r are depressed in a capillary tube. 




Elevation of a wettin- liquid. : . i ( 



86 PASSAGE OP WATER THROUGH CREVICES. 

be only six inches long, we might inquire whether the 
water would overflow from its top, or simply remain 
suspended. 

Mathematical considerations as well as direct experi- 
ments prove that, in such a case, there would be no over- 
flow. A capillary tube under these circumstances sim- 
ply lifts the water, but can not produce a continuous 
current. 

But if a removal of the water at the top of the tube 
take place in any manner, as, for instance, by evapora- 
tion, or by being dissolved away, then a continuous cur- 
rent is produced. This fact explains the phenomena of 
endosmosis, presently to be described. 

As illustrative of the production of a continuous flow, 
we may cite the case of a spirit-lamp, the wick of which 
may be regarded as a bundle of capillary tubes. If the 
cover of the lamp be taken off, all the spirit will pass up 
the wick and escape by evaporation ; or, in an oil-lamp, 
the wick of which becomes readily saturated with the 
liquid, but never exhibits any overflow ; on the lamp be- 
ing kindled, the oil is burned off, and a current is at once 
established. 

I have shown that water will pass through a crevice, 
the width of which is less than one half of the millionth 
of an inch. Pores or crevices of such a dimension are 
invisible even with a microscope. 

The proof of this is very readily obtained experiment- 
28 ally. If we take 

a convex lens, a> 
a, of long radius, 
and place it upon 

.nuniui,,.!,™,,,!,-, .j,,._._ .«.,...,„. ,,.„ ..„. ,.,,, mnai a g.] agg pl ane ^ by 

Passage of water through a crevice. . & \. _ ' 

there will be seen 
at the point of contact, c, on looking down upon the ar- 
rangement, a black spot surrounded by a series of vari- 
ously colored concentric circles, the appearance being 
well known among optical writers lender the name of 
Newton's colored rings. At the point of apparent con- 
Can capillary tubes produce a continuous flow of liquid ? What 
is the effect of its removal from the top of the tube? Under what 
circumstances does a continuous flow in a spirit-lamp or oil-lamp 
take place ? Through how small a crevice will water pass ? Ex- 
plain the fact illustrated by Fig. 28 




ENDOSMOSIS AXD EXOSMOSIS. 



87 



tact, <?, the lens and the plane are, as Newton has shown, 
a distance apart of about the one half of the millionth 
of an inch, and from this central point, proceeding out- 
wardly, the distance between the glasses, of course, in- 
creases. If any where at the outer portion a drop of 
water be introduced, it extends itself instantly across all 
the colored rings, reaching even across the central black 
spot. 

The phenomena of endosmosis may be explained as 
follows : If some alcohol be placed in a bladder, the neck 
of which is tightly tied, and the bladder be sunk in a 

Bad of water, a percolation ensues, so that the bladder 
distends to its utmost capacity, and might even be burst. 
Or, which is a better method of showing the result, if, 
instead of tying the mouth of the bladder, a glass tube, 
open at both ends, and a foot or two long, be fastened 
into it without leakage, as the water introduces itself 
through the pores of the bladder to mingle with the 
alcohol, the liquid rises in the glass tube, supposed to 
l>e left in a vertical position, and, when it has reached 
the top of it, overflows. 
To express this inward 
passage of the water the 
term endosmosis was in- 
troduced, and since a little 
of the alcohol simultane- 
ously passes outward to 
mix with tho water, it is 
said to exhibit exosmosis. 

In Fig. 29 is represent- 
ed the endosmometer of 
Dutrochet. It consists of 
a small bladder, a* tightly 
tied to a tube, d, which is 
open at both ends, and 
bent, as seen in the figure 



at c; tho bladder being 
completely filled with al- 
cohol, and" the tube to some such point as d> the arrange- 
ment is to be placed in a vessel of water, e e; almost 
immediately the level of the liquid will be Been to be ris- 

What is meant by endosmosis? Whafl by exosnxMfo! Des crib e 

the endosmometer. 



Fig. 29. 







88 DEPENDENCE ON CAPILLARY ATTRACTION. 

ing, the bend of the tube is reached, and one drop after 
another falls from the open end into the glass, b. And 
this continues until the liquids inside and outside of the 
bladder are uniformly commingled. 

It is to be regretted that the terms endosmosis and 
exosmosis have been accepted by physiological writers, 
for in these results there is nothing more than what we 
should expect from the known principles of capillary at- 
traction. The pores of a bladder, or of any other such 
organic texture, are nothing but short capillary tubes 
into which water readily finds its way, because it can 
wet the substance surrounding the pore. If the bladder 
be distended with air, and sunk under water, although 
the water will fill the pores, it will not exude from them, 
and accumulate in the interior of the viscus, for, as we 
have seen, a capillary tube can not establish a continued 
current or flow. But the case becomes totally different 
when the bladder is filled with alcohol ; for then, as fast 
as the water presents itself on the inner end of the pores, 
it is dissolved away by the alcohol, and the necessary 
condition for a continuous flow is complied with. Mean- 
time, through the pores themselves a little alcohol passes 
in the opposite way by infiltrating through the incoming 
water, provided that the current be not too strong, and 
so endosmosis of the water and exosmosis of the alcohol 
take place, the current of the former greatly preponder- 
ating over that of the latter, and an accumulation of liq- 
uid in the interior of the bladder ensues. 

That in all this there is nothing specially dependent 
on the organic texture employed is obvious from the fact 
that the same results arise when any inorganic porous 
body is used. Vessels of unglazed earthenware, pieces 
of baked slate or stucco, answer the purpose very well, 
as will also a glass vessel with a minute fissure or crack 
in it. 

An incorrect representation of the conditions under 
which endosmosis takes place is often made. It is said 
to depend on the relative specific gravity of the liquids. 
Thus it is stated that the lighter liquid always moves 

What connection has endosmosis with capillary attraction ? Un- 
der what circumstances is there endosmosis into a bladder? How 
is it known that the organic texture is not necessary in endosmosis? 
Is the direction of the motion dependent on specific gravity ? 



FORCE OF ENDOSMOTIC MOVEMENT. 89 

toward the denser, more abundantly than the denser to 
the lighter. The error of this is readily showg by many 
simple illustrations. Thus water endosmoses equally 
well to alcohol, which is lighter than it, and to gum wa- 
ter or salt water, which are heavier. The relation of 
specific gravity has nothing whatever to do with the 
action. 

The force with which a liquid will thus pass through a 
pore to mingle with another liquid beyond is very great. 
I have observed these motions occurring against a press- 
ure of many atmospheres. And, indeed, \n practice we 
have no means of measuring its actual intensity ;. for 
when a pressure of a certain degree has accumulated, 
hydraulic leakage takes place backward through the 
pore, and conceals the true action. 

From the preceding statements respecting capillary 
attraction and endosmosis, we may therefore conclude 
that, whenever a liquid is in contact with a porous body 
the substance of which it can wet, it will freely pass into 
the pores thereof, and, if the necessary conditions for its 
removal are present, will percolate or transfuse with 
very great mechanical power ; that this will take place 
through pores that are not only invisible to the eye, but 
imperceptible by the aid of the microscope; that some 
liquids pass thus with more readiness, some with less, 
the result in these respects depending on the electro- 
chemical relations subsisting between them and the solid 
they are in contact with, and their own force of cohe- 
sion ; that organic membranes present no peculiarities, 
their action arising, not because they are organic, but 
because they are porous; that the so-called selecting 
power is purely physical, as are the separations and ap- 
parent decompositions to which it gives rise. When a 
drop of colored water is put upon chalk, the water sinks 
in. bat the color is left on the surface. When weak al- 
ia tied np in a bladder, the water will escape 
through the pores, and the spirit become anhydrous at 

If we take a fflaafl tube, a n, J* 1 ;,/. 80 (page 00), over 
the lower end of which a piece of peritoneum, or other 
delicate membrane, b A. is tightly tied, and half fill it 

With what force do these motions of liquids take place? How 

may the selecting power of membranes he illustrated P 



90 



SELECTING POWER OF MEMBRANES. 




Fig. so. with litmus water, and then place it in 

a glass of alcohol, c c, the level of the 
liquids inside and outside being adjust- 
ed according to their specific gravity, so 
that there may be no hydrostatic press- 
ure either one way or the other through 
the pores of the peritoneum — as soon as 
the arrangement is completed, if the ob- 
server be so placed as to view it by 
transmitted light, he will see the water 
descending from the pores of the peri- 
toneum in striae and streams through 
the alcohol in a perfectly colorless state. 
The membrane, therefore, has absorbed 
and transmitted the water, but has re- 
fused to the coloring matter a passage. 
It is to this particular experiment that 
allusion was made when speaking of the 
non-coloration of the chyle after certain 
coloring material had been mixed with 
the food. Such illustrations may there- 
fore satisfy us that the selecting power 
of organic porous textures, like that of 
inorganic ones, is dependent on simple physical circum- 
stances. 

In view of all the preceding facts, I therefore regard 
absorption by the blood-vessels as taking place of neces- 
sity, because of the porous structure of those tubes; for, 
though the pores may be too small to be discerned even 
by microscopic aid, they are abundantly large enough to 
permit such a percolation. Whatever material is exist- 
ing in the chyme in a state of solution in water and also 
soluble in the blood, passes through the walls of the 
blood-vessels, and is moved toward the liver, its perco- 
lation being greatly facilitated by the onward motion 
of the blood, in which liquid it is dissolved as fast as it 
presents itself. The double condition here specified must 
be complied with ; the material to be introduced must 
be dissolved in water, and must be soluble in the blood. 
If the latter condition be wanting, the vessels seem to 
manifest a selecting power, absorption not taking place, 

Describe the experiment of Fig. 30. Give a summary of the pro- 
cess of absorption. 



Selecting power of a 
membrane. 



SUMMAKY OF ABSORPTION. — THE BLOOD. 91 

as in the case of litmus, presented above as an illustra- 
tion — a coloring matter which, though soluble in water, 
is not soluble in alcohol, and so can not, under those cir- 
cumstances, pass through a piece of bladder. 

While thus there is an introduction of digested mate- 
rial from the stomach and intestine into the blood, the 
physical principles guiding us in our explanation teach 
us that there must be a percolation of the more watery 
portions of the blood in the opposite direction — that is, 
into the digestive cavity. There is every reason to be- 
lieve that this percolation is to a far greater amount than 
is generally supposed. Under certain circumstances, it 
is a matter of ordinary observation that the water dis- 
charged from the intestine is more in quantity than that 
which has been taken as drink. 

In the description here offered of the function of ab- 
sorption, the agency of physical forces alone has been 
considered, and these I conceive to be abundantly suffi- 
cient to enable us to account for all the phenomena. 



CHAPTER VII. 

OF THE BLOOD. 

Tlie Offices and Relation of Blood in the System. — The 
Plasma and Cells. — General Properties and Compo- 
\f the Blood. — Quantity in the Body. — Coag- 
ulation. — Blood-cells. — TJieir successive Forms. — The 
perfi et t i U. — ![<> matin : its Properties. — Plasma : 
its Composition, and Variations of its Ingredients. — 
Albumen^ 'Fibrin^ F</t, Sugar. — mineral ingredients. 
— Gases of the Blood, — General Function* of the 
4 ingredients of the Blond. — Introduction of 
Oxygen ly the Cells. — Their transient I) "ration. 

It is necessary for the functional activity of every or- 
ganized being that there shall circulate through all parts 
of it a nutritive liquid. In plants it is the sap; in ani- 
mals, the Mood. 

Why e be ■ percolation of water into the digestive cari- 

\ To what extent may this percolation £r<>? What condition is 

necessary for the functional activity of plants and animal-? 



92 OFFICES AND RELATIONS OF THE BLOOD. 

Since the life of plants manifests itself, for the most 
part, in a purely formative result, and involves little or 
no destruction of parts, the circulating current is devo- 
ted almost entirely to nutrition. But in animals, whose 
conditions of existence involve extensive and unceasing 
destruction, the current is burdened with another duty. 
It is also the means of removal of dying or wasted por- 
tions. 

In the first chapter it was shown that about a ton and 
a half of material is required by a man in the course of 
a year, and that in the same period a like amount is re- 
moved from the system. When we reflect that the in- 
troduction and removal of this immense mass is accom- 
plished through the agency of the circulating blood, it 
is obvious that that fluid must be undergoing rapid 
changes. The elements of decay are strained off or ex- 
haled as quickly as they arise. 

Considered in its relation to nutrition, the circulating 
liquid presents many interesting aspects. Each of the 
thousand variously-constituted parts of the body is with- 
drawing the supplies it needs — the muscular, the nerv- 
ous, the cartilaginous, the bony ; and hence there arises 
a general balance in the system, each part making its de- 
mand at a certain rate, and each observing a comple- 
mentary action to all the rest. Many of those phenom- 
ena which, in the infancy of physiology, were regarded 
as instances of sympathy between different parts, are 
clearly dependent on these conditions ; for the develop- 
ment of one part, by abstracting special material from 
the circulating liquid, permits the co-ordinate develop- 
ment of another, or perhaps puts a stop to it. The mi- 
nutest portion of the mechanism is thus indissolubly con- 
nected with all the rest through the medium of the blood. 

Seen as it circulates in the vessels, the blood consists 
of a colorless liquid containing corpuscles. In man, some 
of these corpuscles are white and others red. To the 
liquid in which they float, the designation of the plasma 
is given ; the colored corpuscles, from their shape, are 

What is the difference of function in the two cases ? How is it 
known that the blood changes with great rapidity? In what man- 
ner does the circulation establish connections between all parts ? Of 
what two portions is the blood composed? What is the plasma? 
What are the discs? 



PROPERTIES AXD COMPOSITION OF BLOOD. 03 

called discs or cells. The specific gravity of the blood 
varies from 1.050 to 1.059, the variation being, to a con- 
siderable extent, due to variations in the quantity of the 
cells. The temperature is about 100° Fahr., the reaction 
always alkaline; there is also a faint sickly odor, differ- 
ing in different animals. The cells give to the blood its 
tint of color, and this, in the systemic arteries, is crim- 
son ; in the veins, deep blue. However, the color of ar- 
terial blood depends considerably on the condition of 
miration. An imperfect introduction of oxygen, as 
in hot climates, causes the arterial blood to assume a 
dark color, and the same is observed when chloroform, 
ether, or diluted irrespirable gases are breathed. The 
blood of the male sex is heavier than that of the female. 

Constitution of the Blood. 

Water 784.00 

Albumen 70.00 

Fibrin 2.20 

a 131.00 

1.30 

- tits 6.03 

Extract, urea, biliary matter, etc 5.47 

1000.00 

As to the quantity of blood in the circulation, it has 
been variously estimated. It may perhaps be taken at 
one eighth of the weight of the body. 

A ^hort time after it has been drawn, the blood un- 
dergoes coagulation, and is then said to be composed of 
the serum and the clot. In this state it is sometimes 
spoken of as dead. The plasma of living blood differs 
from the serum of dead in containing fibrin. 

The coagulation of the blood commences within about 
ten minutes after it has been drawn, and the clot under- 
sequent contraction during one or two days. 
Land the physical nature of this singular 
chai may conveniently regard the living blood as 

containing three leading Constituents — an albuminous 
liquid, fibrin dissolved therein, and the cells. The coag- 
ulation arises l tendency of the fibrin particles 
to agglutinate together. As tlii- takes place, the cells 

What Mid components of the Mood? 

What i» meant by the coagulation of the blood ? How long does Hie 
clot contract? From what does coagulation . 



94 COAGULATION OF THE BLOOD. 

are caught in the meshes of the network that arises, and 
a voluminous red clot is the result. So the serum of 
dead blood contains no fibrin, and differs from the plas- 
ma of living blood in that important particular. 

It has been observed that exposure to cold retards co* 
agulation, as does likewise the absence of air, or cover- 
ing the blood over with a film of oil. The condition of 
rest promotes it, as also does the presence of rough or 
angular bodies. Blood will yield up its fibrin readily 
when stirred with a stick. When, for any reason, the 
cells sink more rapidly than usual from the surface of 
the blood, the fibrin of the supernatant portion coagu- 
lates alone, giving rise to a stratum free from the red 
color, and designated the bufiy coat, and on the subse- 
quent contraction, since there are no cells to hinder the 
fibrin, its parts upon this stratum are drawn more close- 
ly together, and the clot becomes cupped. 

By those who accept figurative expressions as an ex- 
planation of physiological facts, the coagulation of the 
blood is said to be due to its death ; some, however, 
have regarded it as an abortive attempt at organization, 
and therefore a manifestation of life. Such contradic- 
tory explanations lose much of their interest when we 
examine the facts of the case critically. I believe that 
nothing more takes place in blood which has been drawn 
into a cup than would have taken place had it remained 
in the body. In either case the fibrin would have equal- 
ly coagulated. The entrapping of the cells is a mere ac- 
cident. The hourly demand for fibrin amounts to 62 
grains ; hence the entire mass of the blood would be ex- 
hausted of all the fibrin it contains fti about four hours, 
and solidification of fibrin must be taking place at just 
as rapid a rate in the system as after it has been with- 
drawn. No clot forms in the blood-vessels, because the 
fibrin is picked out by the muscular tissues for their 
nourishment as fast as it is presented, nor would any 
clot form in a cup if we could by any means remove the 
fibrin granules as fast as they are solidified. 

In entering on a detailed examination of the constitu- 
tion and functions of the blood, our attention will have 
to be directed, in the first place, to the cells. It is suf- 

What circumstances accelerate or retard coagulation ? How does 
the bufiy coat form ? What is the explanation of coagulation ? 



SUCCESSIVE FORMS OF BLOOD-CELLS. 95 

ficient to arrest our thoughts at once when we learn that 
for every beat of the pulse nearly twenty millions of 
these organisms die! Physiology has its wonders as 
well as astronomy. 

In the life of man there are three periods distinguished 
from each other by the nature or structure of the blood- 
cells. Those of the first period originate simultaneous- 
ly with, or even previously to, the heart. These are 
sometimes designated as embryo cells, and in that view 
bear the same relation to those of the second period as 
do the lymph corpuscles to those of the third. They 
are colorless and spherical cells, containing granules of 
tatty material, and having a central nucleus. These are 
developed, by a process of internal deliquescence, into 
cells of the second period, which have acquired a red 
color, and in oviparous vertebrates an elliptical form, 
though in man they are circular. They are flat or disc- 
like in shape, have a diameter of about a 5 * of an inch, 
with a central nucleus of half that size. Sometimes 
they appear to undergo multiplication by division of the 
nucleus. 

These cells of the second period are replaced by those 
of the third, the transition being clearly connected with 
the production of lymph and chyle corpuscles. By the 
end of the second month of foertal existence the replace- 
ment is complete, and the class of cells or discs that has 
now arisen is continued during life. The mode of their 
production is this. The chyle or lymph corpuscle loses 
its granular aspect, and acquires a pale red color, which 
gradually deepens ; the corpuscle becomes smooth, loses 
spherical form, and, condensing, takes on a convex 
lenticular shape, and eventually a bi-concave. While 
this change of structure is going on, the specific gravity 
increases through the condensation, and the develop- 
ment closes by the spherical white granular lymph cor- 
puscle becoming a red, bi-concave, non-nucleated, circu- 
lar, small, and heavy blood disc. 

The cell of the first period is therefore spherical, white, 
and nucleated ; that of the-second, red, disc-shaped, and 
nucleated ; that of the third, red, disc-shaped, bi-concave, 
and non-nucleated. 

long do the discs livr? Bow many different kinds of them 

are there? Under what circumstances docs each kind arise? 



9G THE TERFECT BLOOD-CELL. 

The primordial cell advances in development to dif- 
ferent points in different orders of living beings. The 
blood of invertcbratcd animals contains coarse granule 
cells, which pass forward to the condition of the fine 
granule cells, and reach the utmost perfection they are 
there to attain in the colorless nucleated cell of the first 
period of man. In oviparous vertebrated animals the 
development is carried a step farther, the red nucleated 
cell arising, and in them it stops at this, the second pe- 
riod. In mammals the third stage is reached in the red, 
non-nucleated disc, which is therefore the most perfect 
form. 

This perfect form of blood-cell, as it occurs in man, 
may be described as presenting a flattened shape; the 
bright spot, sometimes seen in the centre, arising from 
a refraction of light due to the form of the disc and not 
to a nucleus. The sac of each disc is elastic, so that it 
can be swollen by water until it becomes convex or even 
globular, or by immersion in thick sirup may be made 
to shrink, effects arising from the endosmotic infiltration 
or exudation through its wall. When passing through 
the fine capillaries in the course of the circulation, the 
cell, by reason of this elasticity, can make its way through 
very difficult passages, extending itself into a cylindroid 
form, but it recovers its original shape as soon as relieved 
from pressure. The average diameter of the cell is esti- 
Fig, 01. mated at 3 2 \> o of an inch, the 

extremes being -^wo an( l 
40* 00 . The thickness of the 
cell is about l2 ^ o Tr of an 
inch. The cell owes its col- 
or to hsematin, which exists 
in its interior in a state of so- 
lution, and associated with 
globulin. 

The facts mentioned in the 
preceding paragraph are il- 
lustrated by the annexed en- 
graved photographs. 7 f 7r/. 

Human blood-colls magnified 500 dkim- 5?- ^ i i i i 

eters. 31 represents human blood- 

Describe the perfect blood disc or cell. Under what circumstances 
may the elasticity of its sac be shown ? How can blood discs pass 
through pores smaller than themselves ? 




FORM8 OF BLOOD-CELLS. 



97 




k 



> 



\ 






J 



©t 




Elliptic blood-cells of fro^ magnified 250 diame- 
ter.-. 



In Fig. 35 (page 98) we 

Fig. 33. 



cells. Their form is 
circular : they have 
a central depres- 

o, l>ut no nu- 
cleus. 

repre- 
ta the elliptic 

nucleated blood- 
cells of the frog, 
with here and there, 
at >/ a, chyle cor- 
Fig. 33 
represents the en- 
dosmotic action of 
water on these cells. 

/. 34 (page 98), 
the action of acetic 
acid in darkening 
or concentrating the nucleus. 
have an illustration 
of the size and ap- 

rance of the 
blood-cell in a rep- 
tile, the photograph 
from which this fig- 
ure was taken hav- 
D made un- 
the same mag- 
nifying power as 
that employed in 
obtaining the pho- 

raph of human 

The cell wall of the 

ner- 

. admitted to be 

fibrin, Of rab- 

:ice allied thereto; but there en much differ- 

ipecting the constitution of the nu- 
lls which possess it. By some, this also 
ded as fibrin; by others, as fat; and by 







the action acid on them ? 

the nature of the cell wall of discs? 

E 



What is 



98 



COMPOSITION OF BLOOD-CELLS. 




Action of acetic acid on elliptic cells. 
Fig. 35. 



Fi 3- 84 - ' others as a species 

of horn, to which 
the designation of 
nucleine has been 
given. 

The cell wall of 
the w r hite corpus- 
cles does not ap- 
pear to be elastic. 
It is viscid, and 
hence these bodies 
tend to agglutinate 
to one another : in 
aspect it is granu- 
lar. The contents 
appear to be an al- 
buminous solution, 
in which fine gran- 
ules are suspended. 
Though we have 
described the mes- 
enteric glands as 
the original place 
of formation of the 
blood-cells, it is to 
be understood that 
these become per- 
fected in the circu- 
lation of the blood ; 
and from what will 
be said respecting 
the function of the 
liver, it may be in- 
ferred that that 
gland is the seat* 
of a most important change : there probably they re- 
ceive their iron. That no special organ is exclusively 
charged with the duty of forming them appears from 
this, that the first form of blood-cells arises in the germ- 
inal area of the embryo when there is, as yet, no gland. 
Leaving the water out of consideration, the predomi- 

Is the cell wall of the white corpuscles elastic ? What connection 
does the liver seem to have with the discs ? 




Eeptile blood-cells magnified 500 diameters. 



COMPOSITION OF IIJEMATIX. 



99 



Fift. 36. 




Dating ingredients of blood-cells are globulin and fa rem a- 
tin. The former is a substance approaching, in proper- 
ties, to casein, or perhaps intermediate between casein 
and albumen. 

ILvmatin is dis- 
tinguished by its 
red color. When 
isolated, it exhib- 
its the changes of 
tint characteristic 
of arterialization 
in a doubtful man- 
ner. There are, 
however, some 
facts which lead 
to the supposition 
that the color of 
arterial and ven- 
•lood does not 
depend so much 
on a chemical 
change in the ha> 
matin as on an al- 
teration of the fig- 
ure of the discs. 
Ibematin contains 
about 7 per cent. 
of iron. 

The crystalline 
itance of blood 
irs under three 
rent forms, in 
is, tetrahe- 
dra, and hexagon- 
al tablets. In the 
prismatic form it 
from 
human, blood, that 
of fishes, and of 

me manfmalfl ; 

!iat substance is globulin related? What are the properties 
of bsematin? Under what forms may the crystalline substance of 
blood be obtained ? 



Human blood-cry BtalB. 
Fig. 37. 




I .;iinra-])i.u'. 



100 



BLOOD-CRYSTALS. 




Blood-crystals of squirrel. 



Fi 9- 3S - in the tetrahedral 

form it is obtain- 
ed from Guinea- 
pigs {Figure 37), 
rats, and mice ; in 
the hexagonal 
form from squir- 
rels. Blood-crys- 
tals are of a red 
color, without 
smell or taste, los- 
ing their water of 
crystallization un- 
der exposure to 
the air, the differ- 
ent forms present- 
ing different rates 
of solubility. 

The crystals may be obtained for examination by cov- 
ering a minute drop of blood with a glass slide, and, aft- 
er adding water, alcohol, or ether, to permit a gradual 
evaporation to ensue. 

The color of the blood, as dependent upon the tint of 
its cells, is asserted to be connected to a considerable 
degree with the form of those organisms as they vary 
from a concave to a convex surface, and not with the 
state of the hsematin. When they are more concave 
they are of a crimson, when of a more convex, of a dark- 
er hue. 

Among the causes which can impress a change on* the 
figure of the blood-cells ought particularly to be speci- 
fied exposure to oxygen and carbonic acid respectively, 
the latter causing them to become more opaque in their 
centre, broader upon their edge, the cell distending ; an 
opposite effect ensuing under exposure to the former. 

Constituted thus of an elastic sac filled with globulin 
and haematin, the cells float in the plasma. They are 
nourished at its expense, and when they die, deliver up 
their contents by deliquescence to it. Accompanying 

Under what forms may the crystalline substance of blood be ob- 
tained ? How is it that the color of the blood may depend on the 
form of the discs ? What ensues under exposure to oxygen and car- 
bonic acid respectively ? 



VARIATIONS IX WATER AND ALUUMEX. 101 

them arc the white corpuscles, from which new genera- 
tions are to arise. It is usually stated that for every 50 
red discs there is one white corpuscle. They may be 
readily discovered during the circulation by the micro- 
pe, many of them occupying the exterior of the cur- 
rent, as though they had a special relation to the soft 
tissues. 

We have next to speak of the plasma. It may be de- 
scribed as a clear and slightly yellowish colored fluid, 
consi>ting, as all animal juices do, for the most part of 
water, holding in suspension or solution albumen, fibrin, 
. and various mineral bodies. 
Of the water it may be remarked, that the usual per- 
centage estimate made of its quantity, as regards the 
entire" blood, is from 700 to 790 parts in 1000. Within 
these limits it is liable to rapid variations, as dependent 
on the condition of thirst or the recent indulgence in 
drinks. It does not increase in proportion to the amount 
winch has been imbibed, for the Malpighian bodies of 
the kidney, as will hereafter appear, strain it ofT with 
it rapidity. When the blood-vessels are distended 
B certain degree, they refuse an entrance to it. The 
necessity of these provisions arises from the fact that 
there is a certain state of viscidity the blood must pos- 
18 for its proper circulation. 

The albumen varies in quantity from 60 to 70 in 1000. 

It is probably associated or combined with soda. It ex- 

- in the blood of the splenic and hepatic veins as the 

neutral albuminate of soda. It is the plastic material 

from which all the soft tissues are nourished, and by it 

the cells themselves grow. Fibrin arises from it in the 

- me manner fis it does during the ineuba- 

i of an egg ; every care is taken to economize it in 

m, and it r excreted except in disease. 

; albumen is greater in venous than in 

rial blood, the proportion increasing during dig 

tion. It also presents variations in different states of 

Its condition varies in various parts of the cir- 

* 

f the red cells and white corpo 
Where do the latter chiefly occur in the Mood current? What is 
the composition of the plasma? To what extent may water vary in 
the blood? How u its quantity diminished? What is the relative 
quantity of albumen ? To U hat extent docs it vary ? 



102 FIBRIN, AND FATS OF THE BLOOD. 

culation, a circumstance, to a considerable extent, due 
to the nature of the salts, or to the quantities of alkali 
with which it is associated. 

The fibrin is usually estimated at 2 or 3 parts in 1000 
of blood. It may fall as low as 1, or rise as high as *I%. 
There is a constant drain upon it for the nutrition of the 
muscular tissues ; and since it originates in the action 
of oxygen upon albumen, we should expect, as is really 
the case, that arterial blood would be richer in it than 
venous. The portal blood contains it in minimum quan- 
tity. Its percentage rises if oxygen be inhaled, or the 
respiratory process be quickened ; for similar reasons, 
it uniformly increases in acute inflammations. 

It has been asserted, as was mentioned before, that 
there is so wide a difference between the fibrin of blood 
and muscular fibre, that we can no longer regard the 
latter as arising from the former, but must consider it 
merely as coagulated albumen ; and that, since the ac- 
tion of acetic acid upon it shows its relation to gelatine, 
it is probably more nearly related to the fibro-gelatinous 
than to the cellulo-albuminous tissues. But, although 
the fact that fibrin contains more oxygen than albumen 
seems to lend weight to such views, since oxidation ap- 
pertains to the retrograde rather than to the ascending 
metamorphosis, there are so many arguments in favor 
of the old doctrine, that I think it may be regarded as 
thus far unshaken. Moreover, it is now established be- 
yond any doubt that by nitrate of potash, and other 
salts, fibrin may be transmuted into a substance analo- 
gous to albumen. 

The fats vary very much in quantity at different times. 
The amount is usually stated at from 1.4 to 3.3 in 1000 
of blood. After a meal the plasma may be actually 
milky, through the fat globules brought in by the chyle. 
We have already shown that starch will give origin to 
fat, and oily substances can be obtained from lactic acid 
itself. The nitrogenized bodies, during their destruc- 
tion, likewise yield them, and it is a normal function of 
the liver to effect the production of fat. 

What is the quantity of fibrin ? What is its proportion in differ- 
ent kinds of blood ? What reasons are there for supposing that fibrin 
is a histogenetic body ? To what extent do the fats of the blood 
vary ? 



CONSTITUENTS OF BLOOD. 103 

Among the special constituents of certain portions of 
the venous blood BUgar ought not to be overlooked. It 
exists as a constant ingredient of the blood contained in 
that part of the circulation intervening between the liv- 
er and the lungs. As liver-sugar it may have originated 
*n the transmutation of cane-sugar, or from the metamor- 
phosis of the muscular tissues. 

The mineral constituents of the blood discharge very 
different duties, some, either directly or indirectly, act- 
ing functionally, others as histogenetic bodies. Thus 
the alkaline properties of the blood are due to the pres- 
ence of the carbonate and phosphate of soda, and this 
latter substance enables the serum to hold in solution 
carbonic acid, and thus it maintains a relation in the 
respiratory operation. But the phosphate of lime dis- 
charges a true histogenetic function, since upon it the 
bony system depends for its nutrition. The mutual re- 
lations of these substances are, of course, very complex, 
though often of importance. Thus, of the two just men- 
tioned, the phosphate of soda enables the serum to hold 
the phosphate of lime in solution. 

The gases which can be disengaged from the blood 
are carbonic acid, oxygen, and nitrogen. This liquid 
can absorb once and a half its volume of carbonic acid, 
and in arterial blood the proportion of that acid to oxy- 
gen is as 1 G to 6, in venous as 16 to 4. That the oxygen 
.cry loosely retained is shown by the circumstance 
that it may for the most part be removed by exposure 
in a vacuum. The other gases may be withdrawn by a 
\m of hydrogen. 
At a temperature of 98°, water absorbs scarcely one 
per cent, of its volume of oxygen gas, but the blood can 
take up from 10 to 13 times as much. This is accom- 
ied by the coloring material. 

lamination of the special constituents 
the blood leads Qfl next to consider the general func- 
tions of this liquid in the aggregate. 

In tl •. the blood discharges the follow- 

er offices. lt< albumen has the duty of giving origin 

In what part of the circulation <l<>r-> liyer-eugar occur? What an 
the chief mineral constituenti of toe blood? What are their func- 
tions? Whal - «1 from the blood? WL 

the relative absorption of oxygen by water and by hlood? 



104 FUNCTIONS OF THE CONSTITUENTS OF BLOOD. 

to all the plastic tissues of the system. From it, for ex- 
ample, by cell actioD, as explained in treating of lacteal 
absorption, fibrin arises — fibrin,. which is used for the 
renovation and repair of the muscular tissues. The 
discs have a relation with the function of respiration ; 
they obtain oxygen in the pulmonary circulation, and* 
carry it through the system. They contribute, more- 
over, to the development of muscular fibre, and also 
nervous material, and this not alone as regards the col- 
oring matter of those tissues. The fats are necessary in 
the production of fibrin and for the nuclei of cells ; but, 
besides these histogenetic relations, they eventually, 
with the exception of liver-fat, undergo oxidation, and 
so minister to the support of a high temperature. Of 
the saline substances, common salt promotes digestion 
by aiding in the preparation of gastric and pancreatic 
juices ; the phosphate of soda enables the plasma to hold 
carbonic acid in solution, and carry it to the lungs. 

It is interesting to observe the limits of variation the 
blood may present in disturbed or diseased conditions. 
In inflammations, the fibrin may increase fourfold ; in 
typhoid fevers it may diminish to less than one half, and 
from these variations special results may arise. Thus 
diminution of its fibrin disposes the blood to preternat- 
ural oozing or facility of escape. So also the discs have 
been known, in cases of chlorosis, to sink to one fifth of 
the healthy amount. The albumen, too, exhibits like va- 
riations. In Bright' s disease it greatly diminishes, much 
of it escaping in the urine by the straining action of the 
kidneys. 

The discs are necessary to the production of a high 
temperature by constantly transferring oxygen from the 
cells of the lungs to every part of the body ; carriers of 
oxygen they have been truly called. That this is one 
of their duties has been proved experimentally, for a solu- 
tion of albumen or the serum has but little power of ab- 
sorbing oxygen, scarcely exceeding water itself in that 
respect, but the discs condense it at once. The change 
of color they exhibit as they alternately gain or lose that 
element is in itself a proof of this fact, as is also the ac- 

What are the general functions of the blood ? To what extent 
may its composition vary in states of disease ? How are the discs 
connected with the production of heat ? 



GRADUAL DESTRUCTION OF BLOOD-CELLS. 105 

tion of serum or blood-discs respectively on a measured 
volume of air contained in ajar. If the discs be in the 
venous or purple condition, they quickly absorb oxygen 
from the confined air, Avhich therefore at once dimin- 
ishes in amount, but the serum, or a solution of albumen, 
produces no such effect. The plasma serves, therefore, 
for the general nutrition of the system, and the discs, 
by transferring oxygen from point to point, discharge 
that part of their duty connected with the production 
of heat. 

But the discs, though of a flattened form, are truly 
cells, and all that obtains in the case of cell life and cell 
action obtains for them. They have not a duration at 
all comparable to the duration of the system, but are con- 
stantly coming into existence and disappearing. Each 
is an individual having its own particular history, its 
time of birth, its time of maturity, its time of death. 
I through a series of incidents proper to it- 
Originating as has been described, they grow at 
the expense of the plasma, and in this regard it serves 
for their nutrition as well as for that of the body gener- 
ally. 

< hi exposing blood-cells to oxygen and carbonic acid 

•s alternately, there is not only a change in their 

ipe, which becomes corrugated and star-like, but also 

in their chemical constitution, so that, eventually, they 

are entirely destroyed. Such alternations occurring in 

the system doubtless lead to the same result, though 

lowly, since the oxygen is presented in a diluted 

condition. 

corrugated and star-like blood-cells abound in 
the fthe portal, though not in that of the hepat- 

ic vein. It' their appearance arises from their tendency 
to di-ii i, this is no more than might be expect- 

in \i<-w of the functions of the liver. That the stel- 
lat. m indication of a commencing disorgan- 

• profound change, may be illustrated by 
an examination of the action of water on normal blood- 
i.ich. if they be exposed to that liquid, undergo 

What i- the * 1 1 1 y of the plasma and tin- discs respectively? In 
what particulars may 1 1 » - - discs be considered as individuals? Dn- 
v.iiat circumsti they become corrugated ? What is the 

r upon them ? 



106 



ASSOCIATION OF HJEMATIN AND OXYGEN. 



Fig. 39. 




Stellated blood-cells magnified 500 di- 
ameters. 



a distention ; their thickness increasing more rapidly 
than their diameter, they lose their concavity, become 
convex, and at last appear as spheres of a less size than 
the original discs. When the quantity of water they 
have received has distended them to their utmost capac- 
ity, they are invisible ; but 
when it is withdrawn from 
them by establishing exos- 
mosis through the addition 
of saline substances, they 
may reappear in the corru- 
gated or star shape, as seen 
in the photograph, Fig. 39. 
With respect to the ac- 
tion of the hsematin, it may 
be observed that other ni- 
trogenized coloring materi- 
als present a similar relation 
to oxygen. As an example, 
indigo may be mentioned. 
I consider that the properties of this substance illustrate 
in a significant manner the properties of ha3matin in the 
system. Indigo occurs in the leaves of the plant which 
yields it, in a yellow and soluble state. It is easily ex- 
tracted from them by maceration in water. Exposed 
to the air, it absorbs oxygen, becomes insoluble, and si- 
multaneously gains a deep blue tint. So lightly is the 
oxygen thus united to it, that by exposure to very fee- 
ble agents it surrenders it up, and repasses into the yel- 
low and soluble condition. Once more exposed to the 
air, it turns blue, and once more may have that color re- 
moved from it by taking its oxygen away. For many 
times in succession its tint may be thus changed, and 
made yellow or blue at pleasure. 

From this we perceive in what a loose manner oxy- 
gen is held by such a coloring material ; how readily it 
surrenders it, and how readily it recovers it. Such a 
union can scarcely be called an oxidation or a combina- 
tion ; it is rather an association. 

All this is precisely what occurs in the case of hsema- 
tin. It takes up oxygen with rapidity as it goes over 

What are the changes in color which indigo may exhibit ? What 
analogy is there between that substance and heematin ? 



-OCIATION OF II.KMATIX AND OXYGEN. 107 

the cells of the lungs, and turns scarlet; it surrenders 
that oxygen with equal facility as it passes the systemic 
capillaries, and turns blue. This change of color is in- 
ssantly taking place ; it is now red and now blue, as 
the discs are passing in the greater and the less circula- 
tion. 

Formerly it was supposed that, in the act of respira- 
tion, oxygen from the air united with carbon of the 
blood of the cells, and carbonic acid formed, a combina- 
tion or perfect oxidation taking place in the lung. But, 
if this were true, the temperature of those organs should 
be higher than that of the rest of the body, and this is by 
all admitted not to be the case. 

The discs are therefore carriers of oxygen. They re- 
ceive that vivifying principle as they move over the res- 
piratory cells, and, freighted with it, pass to all parts 
of the body, not united with it, nor disorganized, nor 
burnt up by it, but holding it loosely, and ready to give 
it up and go back again for a fresh supply. 
The sac containing the haematin oilers no kind of re- 
ance to these exchanges. It will be fully demon- 
strated in the chapter on respiration that this is the case. 
Thick pieces of India-rubber, stout animal membranes, 
or even masses of stucco, present no obstacle to the pas- 
:'o of gases. The delicate wall of these cells, a tissue 
of almost inconceivable tenuity, can offer no resistance. 
The gas passes in and out without impediment or re- 
:nt. 
But though in this manner these little organisms per- 
form their duty, it is only for a time. They may take 
from the air-cells and give it up in the system, 
and do this perhaps many thousand times, but it comes 
l) end at last. The incessant motion stops, and the 
n and exhausted disc is brought to its term. By 
-teals over it, it becomes corrugated 
and relaxed, is unable to withstand chemical reagents, 
comrades can do. Through the micro- 
mis puckered and attenuated. The red color 
its interior deteriorates into a tawny tint. As with 

D that hamatin ifl not oxidized in the langfl ? Why 

< trrien of oxygen ? Does the buc offer any 
itancetothe reception of oxygen? What eventually becomes of 

them? 



108 CIECULATION OF THE BLOOD. 

a leaf in the autumn, the natural color of which disap- 
pears, and yellowness or other change precedes its fall, 
so with the dying disc. Unable any longer to discharge 
its duties, its existence is brought to a close, the decayed 
haematin is shed out, and gives a transient tawny tint to 
the plasma, but is presently strained off as one of the 
constituents of bile by the liver. Nor is this illustra- 
tion wholly metaphorical, for, in the case of herbivorous 
animals, Berzelius has shown that the coloring matter 
of their bile is identical with chlorophyll, the coloring 
matter of leaves. 



CHAPTER VIII. 

OF THE CIRCULATION OF THE BLOOD. 

The Heart as a Machine. — Inadequacy of Harvey 's 
doctrine of the Circulation. — Physiccd Principle of 
the Circulation ; applied in the case of a Nucleated 
Cell, Pervious Tissue, Motion of Sap and of Blood. 
— Dependence of the Circulation on Respiration. — 
Forms of Circidation : Systemic, Pulmonary, Ported. 
— Description of the Heart / its Movements. — Their 
Force, Number, and Value. — Sounds of the Heart. — 
Cause of its Contractions. — Description of the Arte- 
ries, Capillaries, Veins. — Explanation of the Circula- 
tion of the Blood. — Facts supporting it. — The First 
Breath. 

No function of the animal mechanism illustrates more 
strikingly the doctrine that we must rely on physical 
agents for physiological explanations than that we have 
now to consider, the circulation of the blood. 

We surrender some of the most beautiful recollec- 
tions of classical mythology, and some of the most cher- 
ished popular illusions of our own times. The heart, 
which in the higher classes of life is the central organ 
of impulse of the circulation, is to be degraded into a 
mere engine. We have to speak of its valves, its cords, 
its pipes. We have to consider its exhausting and its 
forcing action — to deal with it just as we should deal 
with any hydraulic apparatus. In the old times this or- 



CIK'TLATION OF THE BLOOD. 109 

gan was looked upon as the seat of the thoughts and the 
passions ; it was the centre of all good and evil, purity 
and uncleanness, devotion and love. In the modern sys- 
tem the brain has succeeded to the functions once im- 
puted to it. * 

The heart, then, is no longer an altar on which flames 
are burning, no longer the seat of the passions and the 
iroe of love. It is a machine, but what kind of a ma- 
chine? How great is the admiration we may express 
at its exquisite construction! This little organ can ex- 
ecute three thousand millions of beats without a stop! 
In the course of a life, such as we sometimes meet with, 
it has propelled half a million tons of blood, and, though 
momentarily wasting, has repaired its own waste all the 
time. The mathematical rhythm of its four moving cavi- 
ties, the perfect closure of its mitral and semilunar valves, 
and the regurgitating play of its tricuspid, have never 
failed it. To the eye of the intellect there is nothing 
in transferring it from the regions of metaphor and 
illation to the domain of physical science. 
The doctrine of the circulation of the blood was first 
propounded by Harvey about two hundred years ago. 
h originated in the discovering of the valves of the veins 
by Fabricius ab Aquapendente. After many years of 
inssion, it was reluctantly received by the medical 
profession. 

In this doctrine the circulation is referred to causes 

that are purely mechanical, in the strictest acceptation 

of that term. The contraction of the walls of the heart 

pels the blood through the arterial tubes, and even 

through the veins, the direction of its movement being 

I by a proper arrangement of valves. 

when comparative anatomy and physiological 

re more extensively cultivated, it was seen 

that thi ifl insufficient, for the unity of nature 

fori lieve that nutritious juices are circulated 

in different tribes of life by different forces. And though 

it may be that the C bionfl of that central impelling 

thanism regulate the circulation in those organisms 

ceptioa have we to entertain of tin the heart? 

ve of the circulation determined Jj Who dis- 

the function of the heart 
in II ie? 



110 PHYSICAL PRINCIPLE OP THE CIRCULATION - . 

which have a heart, what is to be made of those count- 
less numbers having none ? In this group we find the 
whole vegetable creation, and a majority of the animal. 

There is a physical principle that has long appeared 
to me sufficient. Its use in an explanation of the motion 
of nutritive juices in organized systems of every class I 
have taught in the University for many years. It pos- 
sesses the advantage of generality, since it is applicable 
in every case, from the circulation taking place in a 
closed cell up to that of man. 

In Chapter VI. is a general statement of the phenom- 
ena and laws of capillary attraction ; the principle now 
to be employed is closely connected therewith. It may 
be stated as follows : 

If two liquids communicate with one another in a ca- 
pillary tube, for the substance of which they have affini- 
ties of different intensities, movement will ensue : the 
liquid having the highest affinity will occupy the tube, 
and may even drive the other before it. The same ef- 
fect will ensue in a porous structure. 

Fig. 40. Thus, let b 5, Fig. 40, be a 

l jE= g- ^ _ capillary tube of any kind, 

™ occupied conjointly by two 

Motion in a capillary tube. liquids, CI and V, meeting 

each other in the middle, c ; a having a high and v but 
little affinity for the substance of which the tube con- 
sists, a will occupy the tube, pressing out v before it. 
Of course it is to be understood that the liquids a and 
v respectively communicate with reservoirs that can fur- 
nish them a necessary supply. 

The various phenomena described under the designa- 
tion of endosmosis are experimental illustrations of the 
same kind. Thus, when water is put on one side of a 
piece of bladder and alcohol on the other, the water, 
having the highest affinity for the substance of which 
the bladder consists, occupies the pores thereof, and ex- 
pels the alcohol. Nor would any of the latter substance 
find its way in the opposite direction, back into the wa- 
ter, were it not so soluble or diffusible in that liquid. 
Exosmosis therefore takes place through the water, and 
constitutes a subordinate or feeble current. 

On what physical principle does the capillary circulation depend ? 
How does that principle explain endosmosis ? 



ClKtTLATION" IX CELLS. Ill 

Now it is precisely relations of this kind that are ob- 
ved in the case of the circulating and nutritive juices 
of all organic beings. 

The simplest instance is presented by the fluid con- 
tents of certain nucleated cells, both among animals and 
plants, in which a current moves toward, and then from 
the nucleus, coming back in a returning path. The fluid 
which the cell contains yields to the nucleus, in which 
ma to he concentrated all the activity of the organ- 
ism, the nutritive material it requires, and, this done, 
3 on to make way for other portions. The act of 
nutrition, therefore, is followed by motion, and this upon 
the above simple principle ; for the liquid, before it ap- 
proaches to the nucleus, is charged with material which 
the nucleus can attract; but immediately after contact 
taken place, and the material has been removed, the 
liquid maintains -no longer any relation with the nucleus, 
the affinity or attraction is satisfied, and, so to speak, it 
loses its hold thereupon, and is pressed off by new-com- 
ing portions. Before its approach, and after its depart- 
tbe liquid has opposite rela- Fin 41 

tions to the nucleus, and in this 

ct may be regarded as rep- j ] 
nting two liquids, the onehav- [/ 
Bjh affinity, and the other 
the nucleus. The circu- 
lation in vegetable cells is shown j 
by the direction of the arrows in 
.41. The course taken by the 
current may be determined under 
the ope by the minute 

floati rather, drilling gran- 

to and then from the 
nucv 

1 12) represents 

■ 1 hairs from the 

otia Virginica. a, /a c, d 

, .,...,. i table cells. 

SOJ the hair. 
tted lift t) of the current to 

I from tl us. 

juice about to nourish a part has for that part a 

'•s circulation take place in cell-? 
1 ' . . . the illustrai ions, Fi .11 and 12. 




112 



CAPILLARY CIRCULATION. 




, Circulation in Tradescantia. 



Fig. 42. certain affinity, but, with the ac- 

complishment of that nutrition, 
the affinity is at once lost. Thus, 
for instance, in the systemic circu- 
lation, the parts to be nourished 
have a certain affinity for arterial 
blood ; they take from it whatev- 
er their purposes require, and, that 
done, the relation at once ceases ; 
the blood, become venous, has lost 
its hold upon them, and is pressed 
off. We may conveniently de- 
scribe this effect as a pressure of 
the unchanged upon the changed 
liquid. 

The motions of the sap in plants are clearly depend- 
ent on this principle. Leaving out of consideration the 
minor movements taking place for special purposes, or 
at specific epochs in the development, it may be truly 
said that the nutritive changes occurring in the leaf are 
the primary cause of the motion ; for, as the ascending 
sap presents itself on the sky face of the leaf, it receives 
carbon, under the influence of the sunlight, from the air, 
and becomes converted into a gummy, glutinous liquid. 
And just as in the pores of a bladder, or in those of any 
pervious mineral, pure water will drive out gum-water, 
and occupy the pore, so will the ascending sap expel the 
gummy solution from the capillary tubes or intercellular 
spaces of the leaf. As fast as this takes place, the act- 
ive liquid becomes inactive, by itself changing into a 
gummy solution, and the movement is perpetuated. 
And this ensues not only in the leaf, but in every part 
of the plant ; the liquid to be changed presses upon that 
which has been changed, and forces it onward. In this 
manner, motions in various parts and of very great in- 
tricacy will ensue, but all of them, if duly considered, no 
matter whether their seat be in the root or in the bark, 
in the flowers or in the leaves, no matter whether they 
take place in the height of summer or just at the close 
of winter, when the sap first rises, or even in the germi- 
nating seed which is under the ground, and has never 

What is the explanation of the motion in those cases ? Give the 
explanation of the flow of sap. 



CAUSE OF THE CAPILLARY CIRCULATION. 113 

yet been exposed to the light, may, without difficulty, 
be referred to the nutritive change carried on in the 
leaves of the plant under examination, or its parent, by 
the influence of the rays of the sun. 

All this holds good, not only in the nutrition of a cell, 
the more complicated nutrition of the various parts of a 
flowering plant, or even of an animal, but likewise in 
those destructive changes restricted to the latter class, 
and arising in interstitial decay ; for the blood has a 
double duty to perform: it not only serves for nutri- 
tion, but also for the removal of effete and dying parts. 
These it effects the oxidation of, their carbon passing 
into carbonic acid, their hydrogen into water ; and this 
is accomplished by oxygen obtained in the process of 
respiration. The scarlet or arterial blood, charged with 
oxygen, passes to all parts of the economy in search 
of organic particles ready to be removed ; it effects their 
disorganization, and, becoming thereby venous, is press- 
ed onward. And now, if we recall that nutrition in an- 
imals depends on the access of air — even fibrin can not 
M from albumen except under that condition — we can 
not avoid the conclusion that all operations of repair and 
all operations of waste are made to conspire together for 
the production of movement ; and though every part of- 
3 its own special cause, as depending on nutrition, or 
integration, or secretion, they may be all grouped to- 
her as the necessary results of one more primitive 
ration, the supply of oxygen to the blood in the res- 
tory mechanism. 
In my view of this subject, it is therefore the arterial- 
ization of the blood in the lungs which is the cause of 
circulation in man. I consider the circulation as the 
consequence of respiration ; and though, in ono sense, 
e numerous, each portion of nervous 
material, each muscular fibre, every secreting cell work- 
OWU way, these subordinate actions are all refcr- 
lial act, and that is the exposure of 
lood to the sir. 
Whatever, therefore, interferes with respiration, inter- 
ith circulation. If an irrespirable gas ia thrown 
fthe lungs, the passage or the blood is 

in upon the same principle* the capillary circulation ofani- 
i sit that the circulation Is connected with respiration? 



114 OBJECTS AND COURSE OF THE CIRCULATION. 

instantly arrested, and asphyxia ensues. Or, if the ac- 
cess of the air is cut off, as in drowning, in vain the heart 
exerts its utmost convulsive throb — it is unable to drive 
forward the blood ; and in those cases, by no means in- 
frequent, yet undoubtedly the most surprising occurring 
in the practice of medicine — restoration from death aft- 
er drowning, the whole success turns on one condition, 
the re-establishment of the arterialization of the blood. 
If that be accomplished, the circulation is restored, and 
the heart proceeds with its duty. And for these rea- 
sons, I believe that in many cases success would be had, 
where failures are now experienced, if, instead of resort- 
ing to atmospheric air, pure oxygen gas or protoxide of 
nitrogen were administered. 

In the more highly-developed organisms the objects 
of the circulation are threefold : 1st. To minister to the 
nutrition of the system ; 2d. To introduce oxygen ; 3d. 
To remove the products of waste. In man, these vari- 
ous results are accomplished by several different ar- 
rangements : 1st. The greater, or systemic circulation ; 
2d. The less, or pulmonary circulation ; 3d. The portal 
circulation ; 4th. The Malpighian circulation, etc. 

The course taken by the blood is as follows. Leav- 
ing the left ventricle of the heart, it passes into the aorta, 
and is distributed by the ramifications thereof, constitu- 
ting the systemic arteries, to all parts of the system. It 
moves onward through the capillaries, which may at once 
be considered as the terminal ramifications of the arte- 
ries and the commencing tubelets of the veins. These, 
converging into larger and larger venous trunks, the sys- 
temic veins, deliver it into the ascending and descending 
venae cavas, from which it flows into the right auricle, 
and from thence into the right ventricle of the heart. 
From thence it is driven into the pulmonary artery, to 
be distributed to the lungs, and, coming therefrom along 
the pulmonary veins, reaches the left auricle, and from 
thence it gains the left ventricle, which was its starting- 
point. 

In the pulmonary veins, the left cavities of the heart, 

What is the essential point in restoring the circulation after drown- 
ing ? What are the objects of the circulation ? What is the gener- 
al course of the blood in the systemic circulation ? What is it in the 
pulmonic ? 



THE rOKTAL CIRCULATION. 115 

and in the systemic arteries, the blood is crimson. In 
the systemic veins, the right cavities of the heart, and 
pulmonary artery and its branches, it is blue. The 
change from crimson to blue takes place in the systemic 
capillaries, and from blue to crimson in the pulmonary. 
The svstemic, or greater circulation, is considered as be- 
ginning at the left ventricle and ending at the right au- 
ricle ; the pulmonary, or less circulation, begins at the 
right ventricle and ends at the left auricle. This double 
course is sometimes illustrated by likening it to the fig- 
ure 8, the upper loop representing the pulmonary, the 
lower the systemic circulation, the heart being placed at 
the nodal point. 

A- has just been remarked, there are other subordi- 
nate circulations, but of these only one need attract our 
attention at present — it is the portal. This originates 
in a system of capillaries, the veins belonging to the di- 

stive apparatus, which, converging rapidly together, 

m a common trunk, the portal vein. This at once 
ramifies like an artery in the substance of the liver. 
From the resulting capillaries, the blood passes into the 
commencing capillaries of the hepatic veins, which empty 
into the inferior vena cava, and so it reaches the general 
circulation. The physical peculiarity of the portal cir- 
culation is, that it commences in a capillary system, and 
ends in one, without the intervention of any central or- 
gan of impulse, or heart. At a very early period, com- 
parative anatomists were struck with the analogy be- 
tween the portal circulation in man and the systemic 
circulation of fishes, both being carried on in the same 
way. that is, without a heart. In fishes, the heart is a 
branchial, respiratory, or pulmonary one. Their syste- 
mic circulation, or circulation of crimson blood, com- 
mences in the capillaries of the respiratory apparatus, 
gillfl ; a convergence takes place into an aorta, which 
ramifies inl mic capillaries. So the great circu- 

lation in these tube- mplished without any heart. 

It is Bcarcel; jary to point out the bearing of such 

the theories of the movement of the blood. 

In Fig. je 116) is a diagram of the circulation 

nd where bloc ? What i< the | 
circulation? What i> itfl physical peculiarity? In what respect 
docs the portal circulation resemble the systemic of fishes? 



116 



ORIGIN OF THE HEART. 



of a fish ; a is the auricle ; 5, the ventri- 
cle ; c, the branchial or pulmonary artery ; 
6, 6, the branchial or pulmonary veins, 
bringing blood from c?, the branchia?, and 
■e converging directly toy, the aorta, which 
distributes the systemic blood. This is 
collected into a vena cava, g, and so 
brought to the auricle, a. There is, 
therefore, no systemic heart. 

The farther discussion of this subject 
will be continued as follows : We shall 
describe, 1st, the construction and action 
of the heart ; 2d, of the arteries ; 3d, of 
the capillaries ; 4th, of the veins. We 
shall then present a view of the com- 
bined result of these various mechan- 
isms. 

1st, The Heart. The first appearance 
Diagl cuiation! h **" °f tne heart is as a cavity arising in a col- 
lection of cells by deliquescence or sepa- 
ration of the central ones. At this early period, and 
even before the cavity has fairly formed, pulsation may 
be observed. The organ soon assumes a tubular form ; 

and this, becom- 
ing curved, as 
shown in Fig. 44, 
differentiates into 
three compart- 
ments, with arte- 
rial and venous 
3, 




Fig. 44. 







2, the auricle ; 



Rudimentary heart. 

connections ; 1, the venous trunks m 
the ventricle ; 4, the bulbus arteriosus. The form to be 
evqfltually assumed is foreshadowed in the manner in 
which the curved tube develops, the arch of the curve, 
2, bulging so as to form a conical ventricle. This tri- 
chambered heart remains permanent in fishes, as seen in 
the preceding figure (43), of which c is the third cham- 
ber. But in birds and mammals, the aortic bulb merges 
into the ventricle, through which, as well as through the 
auricle, a septum or partition is established, and thus a 
' double heart, or one of four chambers, arises. 



Describe Fig. 43. 
heart? 



What is the mode of development of the 



STRUCTURE OF THE HEART. 



117 




The diagram, Fig. #fc *>. 

45, represents a double- 
chambered heart, d be- 
ing its auricle, e the ven- 
tricle, c a, the veins con~ 
verging to the auricle, 
a the aorta or main ar- 
tery passing from the 
ventricle. The course 
of the blood is indicated 
by the arrows. 

The heart with four 
cavities may be consid- 
ered as arising from the 
conjunction of a pair 
of the preceding form, 

with their efferent and Diagram of single heart. 

afferent tubes, or arteries and veins, so modified or ar- 
ranged that the right heart receives its blood from the 
item in an auricle, from which it passes into a ven- 
tricle, and thence to the lungs. From the lungs, after 
aeration, this blood is Fi 46 

brought to the auricle of 
the left heart, thence into 
its ventricle, and thence 
to the aorta. Though all 
four chambers are gener- 
ally coalesced into one 
conical form, the heart of 
the dugong, Fig. 46, pre- 
sents the true typical 
structure ; E is the right 
or pulmonary ventricle, L 
the left or systemic ven- 
tricle, their apices being 
quite apart; D is the right 
or systemic auricle, F the 
pulmonary artery, K the left or pulmonary auricle, and 
A the aorta. 

rnally, the heart is covered by a serous mem- 

ribe the digram, /■'>'/. 1". How may the four-chambered 
heart !><• considered as arising? What i.^ there peculiar in the heart 
of the dup 




Heart <>f tin- dugong. 




118 COURSE OF THE BLOOD IN THE HEART. 

brane, pericardium, and in its interior is sheathed by the 
endocardium, an extension of the interior coat of the 
great blood-vessels. Though its movements are wholly 
involuntary, its muscular fibres are of the transversely 
striated kind. They are about one third less in diame- 
ter than those of voluntary muscles generally, and are es- 
Fig. 47. pecially characterized 

l^^fc^^ by their disposition to 

anastomose with one 
another, as represent- 
\ ed in Fig. 47. In the 
j ventricles the arrange- 
ment is such that the 
j fibres of the external 
W^tSSSm mm^^^ ^tt^^^fi SA and internal surfaces 

Muscular fibres of the heart. deCUSSate. 

The motions of the heart consist in the dilatations and 
contractions of the muscular walls of its cavities. The 
two auricles contract at the same moment, as do also the 
two ventricles, but the contractions of the auricles coin- 
cide with the dilatations of the ventricles. 

The course of the blood through the heart is this. 
The venous blood, brought by the ascending and de- 
scending cavae, flows into the right auricle as it is dilat- 
ing, and for the moment pushes forward to the ventri- 
cle, but the auricle, being of less capacity than the ven- 
tricle, is filled to distention first ; at this instant it con- 
tracts, forcing its contents past the tricuspid valve into 
the ventricle, and fills it completely. The blood can not 
regurgitate into the veins to any extent while this is 
going on, because of the almost perfect closure of their 
valves. The right ventricle now commences to con- 
tract ; its fleshy columns shorten so as to pull upon the 
tendinous cords attached to the flaps of the tricuspid 
valve : this enables the blood to get behind them, and 
they quietly close the aperture between the auricle and " 
ventricle ; the closure is not, however, under all circum- 
stances, perfect, the mechanism being such as to permit 
leakage or regurgitation to a limited extent. The blood 

What is there peculiar as respects the muscular fibres of the heart? 
In what order do the dilatations and contractions of the auricles and 
ventricles take place ? Describe the course of the blood through the 
heart. 



COURSE OF TIIE BLOOD IN THE HEART. 119 

now rashes into the pulmonary artery, passing by its 
semilunar valves, which, the moment the ventricular 
pressure ceases, shut, so as to prevent any return to the 
heart. 

Having passed through the lungs and been submitted 
to the air, the blood now returns to the left auricle, and 
is forced by it into the left ventricle, the action on this 
side of the heart being the same as on the other; the 
mitral valve, closing the opening from the auricle into 
the ventricle, is worked in the same manner as the tri- 

spid, and the blood is pressed into the aorta, the semi- 
lunar valves of which, at that instant, shut abruptly with 
an audible sound, and prevent any 'regurgitation. In 
this manner the distribution to the system is accom- 
plished. 

On both sides of the heart, as soon as the auricles 
have finished their contraction, they begin to dilate, and 
continue to do so during the period that the ventricles 
are contracting. Thus there is an accumulation in them 
when the ventricles are ready to dilate, and, as soon as 
that occurs, the blood flows freely forward into those 
cavities, the complete distention of which is then accom- 
plished by the contraction of the auricles, as before ex- 
plained. 

The mode of action of the two sets of cavities is dif- 
ferent. The auricles contract suddenly, first at the place 
of junction of their veins, the effect passing quickly for- 
ward ; the ventricles contract more slowly, but simulta- 
neously in every part. 

Daring each beat of the heart two sounds may be 
heard, followed by a silence. The first sound is dull ; 
the second, which follows it quickly, is sharp. They 
may he imitated by articulating the syllables lubb, dup. 
hit* to the contraction of the muscular fibres 
of tire ventricles, and the striking of the apex of the 
heart against the wall oft lie chest; to a certain extent, 
ning of the semilunar valves, and the rush of the 
blood into the pulmonary artery and aorta Contribute to 
it. The b< '»nd BOtind ifl due to the shutting of the seiui- 
lunar valves of the aorta and pulmonary artery. 

rribe the manner in which it< ralrefl work. In what manner 
do the auricles and ventricles respectively contract? What sounds 
arc emitted? Whal is the cause of 



120 MOVEMENTS OF THE HEART. 

At each contraction of the ventricles the heart strikes 
against the walls of the chest, usually between the fifth 
and sixth ribs, and an inch or two to the left of the ster- 
num. This motion is partly due to the action of the spi- 
ral muscular fibres of the ventricles, which gives a tilt to 
^the heart, and partly to the globular form the whole or- 
gan suddenly assumes. 

The number of pulsations made by the heart differs 
very much at different periods of life : at birth it is from 
130 to 140 per minute ; at the seventh year, from 80 to 
85 ; during mature life, from 70 to 75 ; and in old age, 
from 50 to 65. In females it is more frequent than in 
males. It observes a general relation to the number of 
respirations, five pulsations commonly occurring during 
one respiration. It varies with incidental circumstances. 
During sleep it declines in frequency ; after eating, or 
during exercise, it is quickened. Examined from morn- 
ing to evening, it becomes slower by degrees. Lying 
down, the pulse is slower; in a sitting posture, more 
frequent ; and still more so when standing, the varia- 
tions depending on muscular exertion. In conditions 
of disease, the ratio between the number of pulsations 
and respirations is variable. 

The walls of the left ventricle are twice as thick as 
those of the right, and the force of its contractions is 
about double. The capacity of the two ventricles is 
nearly the same, and is *taken at about three ounces. 
The active force with which the auricles dilate is feeble, 
and wholly incompetent to exert any thing like the suc- 
tion power at one time supposed, yet that they are not 
distended by the mere influx of the blood is satisfacto- 
rily proved by their dilatation after the heart has been 
cut out. 

With respect to the absolute force which the left ven- 
tricle exerts for the propulsion of the blood into the sys- 
temic arteries, it is stated to be 13 lbs. This result is 
derived from the consideration that the pressure of the 
blood in the aorta is about 4 lbs. 3 oz. 

That the motions of the heart can not be referred to 
the presence of the blood, or any reflex action arising 
from the cerebro-spinal system, but must be attributed 

What is the number of pulsations? How do they vary? What 
is the absolute force of contraction of the left ventricle ? 



CAUSE OF THE MOTIONS OF THE HEART. 121 

to the organ itself, is proved by their continuance after 
its excision from the body, or even after it has been cut. 
in pieces. Some have supposed that the minute sympa- 
thetic ganglia with which it is furnished are the source 
of the motive power; others are disposed to impute it 
to a self-contractile power of its muscular fibres, irre- 
•tive of any nervous agency. Of course, it is admit- 
ted by all that the brain and spinal cord can influence 
these movements, but such eilects are superadded and 
not uniform. 

Of these opinions, we shall find many reasons for pre- 
ferring the first when we come to the description of the 
nervous mechanism. It will be then seen that one of 
the prominent functions of nervous ganglia of a certain 
order, and particularly the ganglia of the sympathetic, 
is the storing up of impressions they have received, and 
thus becoming reservoirs or magazines of force. The 
power thus engendered or contained in them is by no 
means always delivered out in totality at once, but it 
may be in small portions, at intervals, for a long time ; 
and doubtless in this way the minute sympathetic gan- 
glia of the substance of the heart retain a power of keep- 
ing up the motions of that organ for a certain period of 
time, even though great lesions or morbid changes may 
have supervened. Such a mechanism recalls the man- 
ner in which chronometers are kept going during the 
short time that the action ofHhe main-spring is taken 
off when the watch is wound up. 

2d. The arteries are tubes consisting of different tu- 

- or layers variously numbered by anatomists. They 
may be sufficiently described as, 1st. The exterior tunic, 
containing fibres generally running lengthwise, connect- 
ive and elastic tissue : it is of about the same thickness 

'lie tunic below ; 2d. The middle tunic, characterized 
by being composed of non-striated muscular fibres cir- 
irly arranged ; 3d. The interior tunic, thin, and con- 
of a cellular or epithelial layer, smooth and pol- 
ished, to permit of the ready passage of the blood. 

The ity of the arteries enables them to sustain 

the sudden action of the heart by distending to a certain 

rhal nervous influences do the motions of the heart depend? 

* i> the mode <>t'M<-tiuu of its ganglia? Of how many tunics arc 
the arteries compos 

!■' 



122 THE AETERIES — THEIR ACTION. 

degree as the blood is driven into them, and by their 
■ gradual collapse when the ventricles cease their press- 
ure, the jetting or intermitting flow is converted event- 
ually into a continuous stream. The mechanical influ- 
ence of the heart is thus decomposed into two portions : 
one, of momentary duration, or, at all events, lasting only 
so long as the ventricle contracts ; and a second, occu- 
pied in distending the elastic arterial tube ; but this por- 
tion is not lost to the circulation, since the tube, as it 
contracts, yields it back again to the blood. The mo- 
mentary impulse of the heart is thus spread over a con- 
siderable duration without loss. 

The muscularity of the arteries is shown by their con- 
traction on exposure, their subsequent dilatation being 
due to their elasticity, this contractile property being 
continued for some time after death. It is alio proved 
by the great diminution of diameter the arteries exhibit 
when under the influence of an electric current. The 
quantity of muscular and elastic tissue in different arte- 
rial tubes is usually in an inverse proportion. In the 
great arteries the elastic tissue abounds, in the smaller 
the muscular increases. By their muscular coat the 
quantity of blood in these tubes can, within certain lim- 
its, be regulated. 

At each injection of blood into it an artery distends. 
It then contracts, and thus gives origin to a pulsation. 
Its'increase is both in diameter and length, the tendency 
being to lift it at each pulsation. The distention does 
not occur at the same instant in all these tubes, but those 
nearest to the heart yield first, and the more distant a 
little later. There is, therefore, what may be termed a 
wave of distention passing throughout the length of 
each arterial tube, and another actual wave in the blood 
itself. These pass onward at different rates of speed. 
The interval of wave-motion from the heart to the wrist 
is about one seventh of a second. Of course this wave- 
motion is to be distinguished from the absolute move- 
ment of the blood, which is much slower. In the caro- 
tid artery the flow of the blood is about one foot in one 
second. 

What is the effect of their elasticity ? How may the muscularity 
of the arteries be proved ? Describe the action of an artery as the 
blood flows into it. What is meant by the wave-motion ? 



THE CAPILLARIES. 



123 



A pressure or impact, communicated to a liquid in a 

long tube, is transmitted to the more distant end with 

vastly more rapidity than the liquid itself could flow 

throttgh the same distance. Thus, if we were to sup- 

a very long metal tube to be filled completely with 

water, its two ends having been tightly closed by tying 

pieces of bladder over them, the tap of a finger on one 

of the pieces of bladder would be almost instantly felt 

by a linger laid on the other. Indeed, it has been pro- 

stablish telegraphic communication on this 

principle, though such attempts would prove abortive 

from the interference of collateral circumstances. This 

mple may serve, however, to illustrate the essential 

difference between the flow of a liquid in a tube and the 

of a pulsation through such a liquid contained 

in such a ftihe. 

The capillaries may be regarded as tubular con- 
tinuations of the arteries and the commencement of the 
They ramify through the organic structures. 
They arc of pretty uniform diameter, and may there- 
looked upon as cylinders. Their usual size is 
il t thmttt ot'txn Ifich ; their mode of distribution varies 
with the* structure and functions of the part they oc- 
cur in : thus, in Fi<i. 43. 
muscles they run 
parallel ; in the 
papilla they are 

ist es- 
a deli- 
structureless 
mem 1 analo- 

cell mem- 
brane, and th< 

ama of volun- 
tary muscles. It 
irtain 
astio- 

and tner< 

nuclei. 

the impact of the bluud be illustrated? Describe the 

caj.ilh 




11- membrane of 



124 



THE CAPILLARIES. 




Fi v- 49 - The interspaces be- 

tween adjacent ca- 
pillaries vary much 
in size and shape, 
the latter variation 
being dependent on 
the mode of distri- 
bution, whether 
parallel, reticulated, 
looped, etc. ; as to 
size, in the liver the 
interspaces are of 
less diameter than 
the capillaries, in 
the choroid coat 
still smaller, but in 

Capillary distribution to villi of duodenum. £}]q Cell Ilia. V COat of 

the arteries they are ten times larger than the vessels. 
These interstitial spaces are nourished by the matter 
exuding through the thin walls of the capillaries. 

Fig. 50 represents the capillary circulation in the web 
of the frog's foot : a, venous trunk ; b 6, branches of ve- 
nous trunk ; c c, pigment cells. The elliptical blood- 
discs are seen in outline in the interior of the vessels. 

The blood flows through the capillaries in an uninter- 
rupted stream, its jetting motion being entirely lost. 
The rate of circulation through the systemic capillaries 
is about three inches per minute, that through the pul- 
monary being five times as swift, the length of the ca- 
pillary tube to be passed -^ of an inch, so that the pas- 
sage from the artery to the vein may be accomplished 
in less than one second. It is to be remarked, however, 
that all parts of the cylindrical stream do not move with 
equal rapidity. Those parts nearest to the wall of the 
vessel are spoken of as the still layer, from their tardy 
movement. It is in this that the white corpuscles may 
be seen. 

Fig. 51 shows a portion of a small vessel from a frog's 
foot : a a, red blood elliptic cells, occupying the axis of 
the vessel, and exterior to them, moving more slowly, or 

How does their distribution vary ? How are the interstitial spaces 
nourished ? Does the blood move in a jetting way in the capillaries ? 
What is the still layer ? 



THE VEINS. 



125 



Fig. 50. 




Capillary circulation of frog'.s foot. 

occupying the still lay- Fig. si 

er, the white spherical 
: h 6, nucleated 
epithelium. 

4th. The VEINS have 
a structure in some re- 
lifferent from 
of the arteries. 
Their elastic coat is 
by do nn much 

loped, and their 
Hilarity less dis- 
tinct. With th< 

on of those of the 

js, abdominal vis- 

I brain, their 

interior is furnished 

with vab ingle, 







ibe the structure of the reins. AYhat veins hare no valves? 



126 



STRUCTURE OF THE VEINS. 



Fig. 52. 



Valves of veins open. 
Fig.. 53. 




Valves of veins shut. 



double, or triple flaps, in all instances opening toward 
the heart. The blood flows equably in them, the pulsa- 
ting action of the ventricles having disappeared in the 
capillaries. Since they present an aggregate capacity 
two or three times that of the arteries, the motion of 
the circulation in them is proportionably slower. Fig. 

52 is a diagram show- 
ing the manner in which 
the valves open when 
the blood flows in the 
course indicated by 
the arrows. Fig. 53 
shows their applica- 
tion to each other, or 
to the sides of the 
vein, and the consequent bulging of that vessel when 
the current, as indicated by the arrows, is in the oppo- 
site direction. 

Having now described the structure and action of the 
heart, the arteries, capillaries, and veins respectively, as 
far as is necessary, it remains to group those actions to- 
gether, and present the theory of the circulation at one 
view. 

But, before entering on this, it is proper to offer an 
argument against the doctrine of those physiologists 
who still maintain that the circulation is wholly depend- 
ent on the heart, and that that organ is entirely compe- 
tent to carry it on. 

The majorit3 f of the circulations we examine in organ- 
ic forms are accomplished without any heart. Plants 
have none ; fishes have no systemic heart ; even in man, 
at the first period of embryonic existence, there is no 
such central organ ; in his adult condition the portal cir- 
culation has none. The current of blood in the capil- 
laries, seen under the microscope, exhibits no jetting 
movements, but, on the contrary, a steadiness of flow, 
sometimes for long in one channel, then a cessation, then 
perhaps a retrogradation, and then a new path. It looks 
as though the blood was flowing spontaneously, and not 
by any force acting behind. The heart of an animal 

In what direction do the valves open ? Does the action of tfie 
ventricles reach the veins? Mention some facts proving that the 
heart is not the sole cause of the circulation. 



ION OF THE HEART. 127 

may be suddenly cut out, and yet the capillary motion 
may go on in the same direction as before. After death 
the* arterial tubes are most commonly found empty: a 
;lt whirh is a meehanieal impossibility on the suppo- 
■11 that the heart alone drives the blood, but a neces- 
[uence if the capillaries draw it. In acardiac 
raon8t%S the blood circulates without difficulty, and, 
though it was at one time supposed that in these twins 
the hearted foetus drove the blood through the heart- 
a one, this is now demonstrated not to be the case, 
circulation, moreover, varies locally, and at special 
•lis, as in the development of the generative organs, 
the mammary glands, the flow to the erectile tissues. 
Ubi irritatio ibi lluxus is an old medical aphorism, and 
these local variations are incompatible with the action 
of one central unvarying force. In cases of spontane- 
3 gangfl^e, it sometimes occurs that the circulation 
through the part has declined, while the capillaries are 
all i a subsequent examination proves. The appli- 

ion of cold to a part checks the circulation through 
it, and this not through any contraction of the vessels ; 
likewise, does a jet of carbonic acid gas directed 
upon them. Moreover, any retardation in the supply 
of air to the lungs restrains the circulation, and this not 
alone in the pulmonary vessels, but also in the systemic 
capillaries, producing an increased pressure in the arte- 
rial tubes, a diminished one simultaneously occurring in 
and if, in the various cases now mentioned, 
propulsive action of the ventricles can not be relied 
<>n to explain the difficulties, neither can any supposed 
tion or exhausting action of the auricles. When a 
is tied round a vein, the action of the auricle is 
. but the vein distends beyond the obstruction, 
wing that th( force acting from the capillaries. 

able tu' are, would at once 

collapse under the exertion of a very moderate suction 
isity than would be necessary to 
draw the blood in the v< 
In spasmodic asthma, and in all pulmonary eonges- 
te right ride of the heart circulates the blood 

d tli" heart i^ remov 
insulation ? What i> tli«' ctVcct of 
tare? What i.^ remarked in pulmonary codj 



128 ACTION OF THE HEART. 

with difficulty through the lungs, showing the existence 
of a great obstruction to its motion through the pulmo- 
nary capillaries. An examination of the condition of 
the various portions of the circulatory apparatus after 
death presents facts utterly inexplicable on the doctrine 
of the sufficiency of the heart. I have already mention- 
ed the empty state of the systemic arteries ; to tltis may 
be added what is often witnessed — the distended condi- 
tion of the pulmonary artery, into which the blood has 
been forced by the expiring beats of the right ventricle, 
but has been unable to get through the pulmonary ca- 
pillaries because of the cessation of respiration ; but in 
other cases, where respiration has come to an end more 
tranquilly or slowly, the left auricle is full of blood, 
which must have been driven into it by the pulmonary 
capillaries. In sudden death, as by hanging and drown- 
ing, the right heart is excessively distended^ as is also 
the pulmonary artery. 

I might proceed to add to these other facts exhibiting 
local variations of the supply of blood in the periodici- 
ties of the system. There is a certain amount sent to 
the brain during the day, and a less during the repose 
of the night ; in the muscular system, during the time 
of its action, the quantity demanded is greater ; in its 
state of inactivity, less. A constantly and invariably 
acting machine, such as is the heart, could by no possi- 
bility adjust these variable supplies. But the cases here 
offered are more than enough, and it remains to be add- 
ed that, though not one of them can be explained on the 
doctrine of the sufficiency of the heart, there is not one 
which does not follow as a necessary consequence of the 
doctrine now to be presented. 

EXPLANATION OF THE CIRCULATION OF THE BLOOD. 

On this view, the circulation is conducted in the fol- 
lowing manner. The left ventricle of the heart impels 
the blood into all the aortic branches, any backward re- 
gurgitation into the auricle being prevented by the shut- 
ting of the mitral valve ; the force employed is decom- 

What is the usual state of the systemic arteries after death ? What 
is the condition of the heart in hanging and drowning ? Can the 
theory of the heart's action explain local variations in the blood sup- 
ply ? Describe the circulation as far as the heart's action extends. 



EXPLANATION OF THE CIRCULATION. 129 

ed into two portions, one part exerting an instanta- 
ffect on the blood in pressing it forward, and 
sing instantaneously, and thus giving origin to the 
pulse ; the second distending the arterial tubes, but not 
being lost thereby, since their. elasticity causes them to 
i,and the semilunar valves at the origin of the 
eing at this period shut, a steady, onward press- 
ure is exerted on the blood; so the quickly-ending ac- 
tion of the ventricle gives origin to two distinct mechan- 
mltfl — a sudden impact and a continuous pressure. 
This suffices to bring the blood to the arterial origin of 
the capillaries, and beyond that point the action of the 
heart may be considered not to extend. 

The relation between the interspaces of the capillaries 
and the blood thus introduced to them continues the 
current. The particular mode in which this relation is 
manifested differs in different parts. The oxidizing ar- 
t i rial blood has a high affinity for those portions that 
have become wasted ; it effects their disintegration, and 
tlun its affinity is lost. The various tissues require re- 
pair; they have an affinity for one or other of the con- 
stituents of the blood ; they take the material they need 
and their affinity is satisfied ; or secreting cells originate 
a drain upon the blood, and the moment they have re- 
moved from it the substance to be secreted, they have 
no longer any relation with it. So processes of oxida- 
. and processes of nutrition, and processes of secre- 
all conspire to draw the current onward from the 
art 1 to push it otit toward the veins; and though 

8 may present themselves in many various 
Is, tiny are all modifications of the same simple 
.1 principle. 

A baa now reached the veins, and is forced 
onward in them by the power that has thus originated 
in I The influence of the heart is here un- 

felt, tiaostingi right auricle is iriappre- 

eia ; . thus pushed onward lVoni the capillaries, it 

pleting its BYBtemic or greater 
circulation. This circulation may therefore be said to 
to the high affinity which arterial blood lias for 
£he od having none: and 1 lie action 

iiation in the capillaries. Describe 

its circulation through the vein-. 

W 2 



ISO EXPLANATION OF THE CIRCULATION. 

of the heart is confined to the filling of the arterial tubes, 
and presenting fresh portions of blood to the capillaries. 

Arrived at the right auricle, the blood flows continu- 
ously into it and the right ventricle for a moment, but 
the ventricle holding more than the auricle, the latter 
cavity is fully distended first. At that instant it con- 
tracts, the valves in the veins shutting, and the blood, 
driven thus forcibly into the ventricle, distends it to 
the utmost. The ventricle, in its turn, now contracts, 
the tricuspid valve shutting, and the blood issues forth 
through the pulmonary artery, its valves then closing. 
At this moment an event occurs which, in these descrip- 
tions, is generally overlooked — an action analogous to 
that of the hydraulic ram. On the shutting of the tri- 
cuspid, the ^vhole column of venous blood would be 
brought to a stop if the tubes containing it were un- 
yielding, and a great force would be generated from 
this stopping of its momentum; but the auricle is ready 
to dilate, and into its cavity the blood, which would be 
otherwise checked, flows. I consider that this safety 
action of the auricle is one of its prime functions. The 
rapidity with which the dilatations and contractions are 
taking place furnish no argument against the occurrence 
of this action. I have a hydraulic ram, the pulsations 
of which may be so adjusted as to exceed greatly in fre- 
quency those of the heart, and, indeed, to give rise to a 
low murmuring sound, and yet, under these circum- 
stances, the lateral' force is so great as to throw a col- 
umn of water more than forty feet high. If it were not 
for the dilatability of the auricles and their yielding tex- 
ture, the veins would burst on the shutting of the tricus- 
pid valve. 

The ramifications of the pulmonary artery bring the 
blood to the capillaries of the lungs, but beyond that the 
influence of the heart is not felt, for now the physical 
principle heretofore described comes again into action. 
The venous blood has a high affinity for the oxygen of 
the air, an affinity satisfied as soon as the blood presents 
itself in the cells of the lungs. Arterialization being ac-. 
complished, the portions to be changed exert a pressure 

Describe its passage through the right side of the heart. What is 
meant by the safety action of the auricle ? Describe the circulation 
through the lungs. 



THE HEART'S ACTIOX. 131 

on those that have changed, and the blood, moving for- 
ward in the pulmonary veins, reaches the left auricle of 
the heart. 

For a moment it passes into the left auricle and ven- 
tricle continuously, but the auricle, being of less capaci- 
ty, tills first. It contVacts as soon as it is completely 
full, and drives its contents into the left ventricle, dis- 
tending it to the utmost. The ventricle now contracts, 
shutting the mitral valve, and the ram-like action is re- 
tted on this side of the heart. But the blood expelled 
from the ventricle is urged into the aorta, its force being 
d, as before described, one part acting instan- 
taneously as an impact on the blood, the other on the 
arterial walls, and on the first moment of the recession 
of the walls of the ventricle the semilunar valves of the 
aorta shut, and this act completes one tour of the circu- 
lation of the blood. 

In this description I have said nothing -of the circula- 
tion in the substance of the heart itself, since it would 
have led to a needless complication. It should be re- 
membered, as an illustration of the working of the phys- 
ical principle here explai&ed, that the motion of the 
blood is contrary in the greater and less circulations, 
compared together. In the former, the current is from 
the crimson to the blue; in the latter, from the blue to 
the crimson side. 

The action of the heart is therefore limited to the fill- 
ing of the arterial tubes, so as to present to the capilla- 
a constant supply of blood. There seems to be but 
little suction force exerted by the auricular cavities for 
emptying of the veins. The valvular construction 
economizes every pressure that the mus- 
cles may exert on them in favor of the circulation, for 
S ich pressure must, by reason of the valves, force 
award to the heart. This is, however, only 
an incidental result of the same character as the inllu- 

of respiration exert. They may 
be properly overlooked in a genera] statement of the 
f tne circulaf 

-. in wliat direction does the blood flow? What is 
ction of the circulation in the 
tern and in the lun--? What is the conclusion a* respects ili< i heart's 

ii ? 



132 THE FIRST BREATH. 

By regarding the affinity between the blood and the 
tissues with which it is in contact as the great primary 
cause of the circulation, we assign a reason for those va- 
rious phenomena which can not be- accounted for on 
Harvey's doctrine : the motions in the embryo ; the pe- 
riodic and local variations ; the portal circulation ; the 
changes in the current, as seen under the microscope ; 
the movement in the capillaries after the heart is cut 
out ; the empty condition of the arteries after death ; 
the phenomena of acardiac foetuses ; local inflammations 
and congestions; the gangrene of parts while their ca- 
pillaries are pervious; the retardation of the current on 
the application of cold or of carbonic acid gas ; the re- 
sults of asphyxia and death by drowning or hanging ; 
the changes of pressure in the arteries and veins respect- 
ively during a check on the respiration ; the vis a tergo 
of the veins ; the effects of a ligature on those vessels ; 
the action of irrespirable gases when breathed, and the 
opposite conditions when oxygen gas or protoxide of 
nitrogen are used. 

Among the striking proofs of the truth of this doc- 
trine, that the primary cause of the circulation is the 
aeration of the blood, I would particularly direct atten- 
tion to the effects which ensue in the moment of birth 
at the first breath. That intercommunication between 
the two sides of the heart, established through the fora- 
men ovale and through the ductus arteriosus, is sudden- 
ly put an end to. But this is not through any change 
in the mechanism of the heart itself, nor because of any 
interruption in the action of the placenta. It is solely 
because of the calling into operation of the principle I 
have been here enforcing. Through the contact of the 
cold air, or other causes, the inspiratory muscles make 
their first contraction and distend the lungs. At that 
instant, the commencing arterialization produces a press- 
ure, in the manner I have explained, of the venous upon 
the now arterialized blood in the vessels of the pulmo- 
nary cells. There is no other possible issue to such an 
action than an instant drain upon the heart. The pul- 
monary or less circulation sets in with full vigor. The 

Mention some of the facts that this doctrine will explain. De- 
scribe particularly the change in the circulation at the first breath. 
How is that change to be explained ? 



TITE FIRST BREATH. 133 

blood is not driven by the heart to the lungs, but drain- 
ed by the Lungs from the heart. If it were the heart's 
action that occasioned this sudden increase of force, be- 
cause of the strain thrown upon it through the shutting 
oft of the influence of the placenta, it is inconceivable 
why the current should not continue to move through 
the great avenues already open to it from the right to 
the left auricle through the foramen ovale, and from the 
right ventricle into the aorta through the ductus arteri- 
osus. The arrest of its motion through these channels 
distinctly establishes that the seat of the new action is 
in the lungs, and the final closure of the foramen and 
shriveling of the duct confirm the correctness of this 
conclusion. 

A doctrine which accounts with simplicity for such a 
long list of miscellaneous facts commends itself to our 
attention at once. There are, however, considerations 
of a still weightier character, compelling us to adopt it. 
The affinity between the blood and the parts it is brought 
in contact with is a chemical fact beyond contradiction. 
The pressures and motions I have been speaking of fol- 
low as the inevitable consequences of that affinity. AVe 
can not, therefore, gainsay their existence in the living 
mechanism, and the only doubt we can entertain is as to 
whether they are of competent power to produce all the 
effects before us. But after what has been already said 
respecting the energy of endosmotic movements dis- 
played against pressures of many atmospheres, we may 
abandon those doubts ; and since we have here a force 
of universality enough, and intensity enough, and in ev- 
ery instance acting in the right direction, it would be 
unphilosophical to look farther, since such a force ?/n/st, 
under these conditions, exist in the physical necessity 

of the force in the capillaries sufficient to account 
eolation ? 



134 OF INSPIRATION. 



CHAPTER IX. 

OF RESPIRATION. 

Respiration introduces and removes aerial Substances. 
— Physical and Chemical Conditions of Respiration. 
— Interstitial Movements of Gases. — Condition of 
Equilibrium in the Diffusion of Gases. — Condensing 
Action of Membranes. — Forms of Respiratory Mech- 
anism. — The Lungs of Man. — Three Stages in the 
Introduction of Air : Atmospheric Pressure, Diffu- 
sion of Gases, and Condensation by Membranes. — 
Variations in the expired Air. — Effect of irrespirable 
Gases. — Nervous Influence concerned in Respiration. 
— Residts of Respiration. 

Since it is essentially necessary to the life of all ani- 
mals that the blood should pass to every part of the sys- 
tem, provision must be made for securing aeration. The 
breathing apparatus is the skin, or some extension, re- 
flection, or modification of it. 

Besides the great duty of originating the circulation, 
respiration is connected with others of equal importance. 
The functional activity of the nervous and muscular tis- 
sues is dependent on their oxidation, and this implies 
the introduction of air. In each animal tribe, moreover, 
it is necessary to keep the temperature up to a specific 
point. This also is accomplished by oxidation, either of 
the disintegrating material passing to waste, or of com- 
bustible substances, such as sugar or fat. 

All organic material, at its death, eventually gives 
origin, under the action of the air, to two products with 
which the function of respiration is mainly concerned. 
These products are carbonic acid and water. With the 
exception of gelatin, the other respiratory elements of 
food — fat, sugar, starch, etc., yield these two products 
alone. The nutritive elements give rise to nitrogenized 

What is the object of the breathing apparatus ? On what does the 
action of the nerves and muscles depend ? With what products of 
decay is respiration concerned? What products do the respiratory 
and nutritive food elements give rise to? 



NATURE OF KESPIRATION. 135 

compounds in addition. The conditions of life are such 
that carbonic acid can not be permitted to accumulate 
in the system, and means have therefore to be resorted 
to for its removal. The introduction of oxygen and ex- 
cretion of carbonic acid are accomplished by the same 
mechanism, the lungs. 

Under its simplest condition, respiration consists in 
the passing of carbonic acid with the vapor of water 
from the system, and the reception of oxygen in ex- 
change. The construction of the apparatus accomplish- 
ing this double duty in atmospheric animals is such that 
it can deal with substances in the aerial state alone. 
Nothing can be introduced through the lungs or escape 
therefrom except it be in the gaseous or vaporous form. 
All those products of disorganization not presented un- 
der this condition must therefore be removed by other 
organs, and this is more particularly done by the kidneys. 

Respiration, like circulation, furnishes us with a signal 
instance of the employment of purely physical principles 
for the accomplishment of physiological purposes. It 
is with the pressure of the atmosphere, the diffusion of 
gases, and the condensing action of membranes that Ave 
have now to deal. These give us so precise and per- 
spicuous an explanation of the act of breathing that it is 
needless to look beyond them; yet on that act depend 
the highest operations of life. 

Of the physical principles now to be dealt with, it is 

unnecessary to say any thing respecting the pressure of 

the atmosphere, since that is well understood; but not 

with the phenomena of the diffusion of gases, and the 

tensing action of membranes. 

If a light gas be placed above a heavy gas in a suit- 
able apparatus, the former, notwithstanding its levity, 
will desoend, and the latter, notwithstanding its weight, 
will rise, and a complete and uniform intermixture will 
lit. 

Thus, if a vial filled with hydrogen be placed with its 
mouth downward over the mouth of a vial of the same 
size containing carbonic acid gas. as shown at A, c,Fig t 
6 \ (page 136), in the course of a few moments the dif- 
fusion will }>(> complete, and if the mixture in either vial 

Witli what class of substances i- respiration connected? How 
may the free diffusion of gases \>c illustrated? 



136 PASSAGE OF OASES THROUGH POROUS FILMS. 



Wig. 54. be examined, it will be found to contain equal 
quantities of the gases. 

Perhaps the most satisfactory method of 
illustrating the passage of gases through bar- 
riers is by taking a porous earthenware cylin- 
der, a a, Fig, 55, drying it perfectly, and ce- 
menting into its mouth an open glass tube, 5, 
three quarters of an inch in diameter, and a 
foot or more long. A wide-mouthed bottle, 
c c, being placed as a temporary cover over 
the porous cylinder, it may be filled with hy- 
drogen gas by displacement ; and if the end 
of the glass tube be put into water contained 
in a reservoir, c?, the water will rush up the 
moment the bottle is removed. When this 
motion is completed, if a jar of hydrogen be 
held over the cylinder, the water will be driv- 
Diffusion of en down with great rapidity, Fig. 55. 

gases. an d a number of air-bubbles 
quickly escape. The extraordinary speed 
with which a gas will flow in and out of 
pores could not be better displayed. This 
rapidity of motion is an element with 
which the physiologist has to deal, as we 
shall presently find. 

Even when the texture of the substance 
is much closer, and the pores of extreme 
minuteness, similar results can be obtain- 
ed, as was shown in the experiments of 
Dr. Mitchell, of Philadelphia, who em- 
ployed thin sheets of India-rubber. If, 
over the mouth of a glass bottle, such a 
thin tissue be tightly tied, and the bottle 
placed in an atmosphere of carbonic acid 
gas, movement at once takes place, a little 
air flowing out of the bottle into the car- 
bonic acid, and so large a quantity of the 
acid passing the opposite way that the In- 
dia-rubber soon swells outward, and event- Diffusion through 
ually caps the bottle like a dome, as in earthenware. 
Fig, 56, at b. Or, if the conditions be reversed, the bot- 

How may it be shown that they can pass through porous barriers ? 
Describe Dr. Mitchell's experiment. 




PASSAGE OF GASES THROUGH TOEOUS FILMS. 137 



Tv 



J 




Diffusion through India-rubber. 



Fig. 5T. 



tie being filled with carbonic Fi '<J- r>G - 

acid, and then exposed to the 

atmosphere, the India-rubber 

will be depressed, as at <7, 

and stretch so as almost to 

sink to the bottom. Such 

experiments therefore prove 

that, even though barriers of 

a very close texture should 

intervene, gases will pass 

through them, and with so 

much force, as Dr. Mitchell 

showed, that many inches of 

mercury might be lifted ; nor 

does the movement cease until the gases on both sides 

of the membrane have the same composition. 

Other substances having a close texture may be thus 
readily permeated. I found that a little bladder of shel- 
lac, blown on the end of a glass tube, permitted the pas- 
sage of the vapor arising from water of ammonia. The 
instan taneousness of these mo- 
tions is, however, most beauti- 
fully illustrated by employing 
soap-bubbles, the liquid nature 
of which excludes the idea of 
pores in the strict acceptation 
of that term. If a bottle, a a, 
Fig. 57, be rinsed out with 
ammonia, and then, by means 
of a piece of glass tube, b 5, 
a soap-bubble, c, be blown 
therein, the air from the bub- 
ble being immediately drawn 
into the mouth without a mo- 
ment's delay, the strong taste 
•lie ammonia is perceived. 
Or if a rod, dipped in hydrochloric acid, be presented 
to the projecting end o*f the trlass tube, copious white 
fun, This therefore shows that vapors will pass 

through barriers having no proper pores, the transit 
taking place instantaneously. 

nst what amount of force can such diffusions take place ? I de- 
scribe the illustration. Fig, 57. How mav it he proved that ammo- 
nia instantly panel throngb the soap-babble? 




tuttftDtaneoof paaugt of 
through films. 



138 PASSAGE OF GASES THROUGH POROUS FILMS. 

Soap films enable us to demonstrate the endosmosis 
of gases in a very advantageous manner, owing to their 
cohesiveness and thinness. If the finger be dipped in 
soap-water, and then rapidly passed over the mouth of 
an empty bottle, so as to leave a horizontal film attached 
across, on exposing the bottle to carbonic acid gas, the 
horizontality of the film is immediately disturbed, and 
it soon swells up into an almost spherical dome. Or if 
the bottle be filled with carbonic acid, and then exposed 
to the air, the film is promptly depressed into a deep 
concavity, and bursts. By these methods the passage 
of all kinds of vapors and gases may be demonstrated, 
oxygen, hydrogen, carbonic acid, protoxide of nitrogen, 
the vapors of peppermint, lavender, and various essen- 
tial oils. 

By many experiments on such different substances, I 
found that the law of equilibrium for gases and vapors 
is the same as for liquids. No matter what the thick- 
ness or thinness of a porous barrier may be, movement 
takes place through it, until the media on its opposite 
sides have the same chemical composition. The ob- 
served action, in particular cases, will therefore altogeth- 
er depend on the circumstances under which the exper- 
iment is made. A soap-bubble full of carbonic acid, ex- 
posed to the air in a closed bottle, collapses only to a 
certain extent when the percentage constitution of the 
air it contains is the same as that of the air in the bot- 
tle, contaminated with the carbonic acid the bubble has 
yielded it. But if the bubble be exposed to the free at- 
mosphere, it collapses almost completely, for now the 
carbonic acid escapes finally away. 

One of the most interesting facts connected with these 
results is the perfect manner in w 7 hich a film of excessive 
tenuity will discharge these mechanical functions. With 
a little care, a film may be obtained so thin as to be in- 
visible except in certain lights, when it presents a vel- 
vety black aspect. In this condition, as Newton has 
proved, it is not thicker than three eighths of a millionth 
of an inch, yet endosmosis takes place perfectly through 
it : it expands and collapses, rises up into a dome, or is 

What is the law of equilibrium in these cases ? Why does a soap- 
bubble containing carbonic acid collapse almost completely in air ? 
How do films of extreme thinness act? 



PASSAGE OF GASES THROUGH POROUS FILMS. 139 

depressed into a concavity, as the circumstances of its 
exposure may be. And this should prepare us to admit 
that in organic tissues of the utmost degree of tenuity 
these physical phenomena may occur, and that even un- 
der these most unlikely circumstances such tissues may 
give origin to mechanical forces of the greatest intensi- 
ty, as we shall now prove. 

The law of the diffusion of gases has but a very lim- 
ited physiological application. The introduction of it 
in cases to which it does not properly apply has led to 
eral errors. There is nothing common in the result 
of the movement of gases exposed freely to one another, 
and exposed with the intervention of a close-pored tis- 
sue. The tissue itself gives origin to mechanical force 
of such intensity as not only to modify the diffusion rate, 
but, in a great many of the most important cases, abso- 
lutely to invert the direction of the motion. Thus, 
through a mass of stucco, in which the pores are of sen- 
sible size, atmospheric air passes more rapidly to carbon- 
ic acid than carbonic acid does to it, but through the 
thinnest film of water the reverse takes place. A bub- 
ble full of that acid, exposed to the air, lets it escape 
with so much rapidity that in a few moments a complete 
collapse has occurred. If the law of diffusion here held 
good, the bubble should rapidly distend. 

Moist membranes and films of water, by reason of 

their chemical affinity for gaseous substances, and their 

icnt condensing action, become the origin of 

at mechanical power. Under such conditions, I 

have shown that carbonic acid passes into atmospheric 

air, driven, as it were, by the action of the membrane 

inst a pressure often atmospheres, and sulphureted 

hydrogen against a pressure of twenty-five atmospheres, 

:m'i. gainst these great resistances, the passage is 

tmplished with so much promptness as to lead to 

rence that a membrane will cause one gas to dif- 
even though the apparent resistance 
be indefinitely great. 

In .//;/. given a representation of the 

arrangement by which these results were obtained. It 

COm rong g]a8S tube, seven inclies or more in 

the law of diffusion applj in tb ainst what 

amount 



140 FORCE OF PASSAGE THROUGH MEMBRANES. 



Fig. 58. length and half an inch in diameter, hermetic- 
ally closed at one end, through which a pair 
of platinum wires, #, c, pass into the interior 
of the tube parallel, but not touching. The 
other end, a a, has a lip or rim turned on it. 
Between the platinum wires, a gauge-tube, r?, 
is dropped, to show the amount of condensa- 
tion. On the top of the gauge-tube a small 
test-tube, f, is placed, to contain a reagent 
suited to the gas under trial, as lime-water for 
carbonic acid, acetate of lead for sulphureted 
hydrogen, litmus water for sulphurous acid. 
Sometimes, instead of this test-tube, a piece 
of paper, soaked in the proper reagent, was 
employed. The large tube was then filled 
with water to the height e e. Its lip or rim, 
a «, being next smeared^with burnt India-rub- 
ber, to insure absolute freedom from leakage, 
a thin sheet of India-rubber was tied tightly 
over it, and over this again, to give strength, 
a very stout piece of silk. Every thing being 
^nfiitratiSn^ tnus arranged, the projecting wires, 5, <?, were 
connected with a voltaic pile, decomposition 
of the water ensued, oxygen and hydrogen being disen- 
gaged, and a condensed mixture of atmospheric air and 
those gases accumulated in the space aaee^the gauge- 
tube showing the extent to which the condensation had 
gone. Now if the little tube,/, had been filled previ- 
ously with lime-w T ater, and the whole arrangement was 
introduced into a jar of carbonic acid gas, the upper 
part of the lime-water presently became milky, and aft- 
er a time a copious precipitate of carbonate of lime sub- 
sided. This would readily take place when the gauge 
was indicating a pressure of ten atmospheres. In like 
manner, when a piece of paper imbued with carbonate 
of lead had been introduced into the tube, and a press- 
ure of 24j atmospheres accumulated, on introducing the 
instrument into a vessel of sulphureted hydrogen, the pa- 
per quickly became brown. Sulphureted hydrogen can 
therefore pass through a sheet of India-rubber and dif- 
fuse into an atmosphere of oxygen, hydrogen, and at- 

Describe the experiment illustrated in Fig. 58. How in that in- 
strument is the force of infiltration measured ? 



GENERAL PKIXOirLES OF DIFFUSION. 



141 



mospherie air beyond, though it is resisted by a press- 
ure equal to that of 800 feet of water. 

The method of condensation here employed, because 
of its freedom from mechanical concussions, enabled me 
to continue these researches up to pressures of 50 at- 
mospheres without leakage, in comparatively slender 
tubes, and even under these circumstances gaseous dif- 
fusion seemed to take place without any restraint. 

It would lead me too far from my present object to 
pursue the consideration of these facts, and I must there- 
fore be content to refer the reader to the memoirs in 
which they have been specially discussed.* 

Under its simplest aspect, the act of breathing con- 
si>ts in the elimination of carbonic acid from the sys- 
tem, and the introduction of oxygen. The manner in 
which the respiratory surface frees itself from the for- 
mer, and secures new supplies of the latter, differs very 
greatly. In the lower aquatic animals currents are es- 
tablished in the water by the aid of ciliary motion, and 
by these the necessary changes are made. In others, in 
which respiration is conducted by the skin, incessant lo- 
comotion is relied on, and again, in others, the water is 
drawn into the stomach and intestinal canal, and every 
part bathed with the aerating me- 
dium. 

In insects, the type of carrying air 
to the blood is developed to the ut- 
3 t degree, there bein^ Grreat num- 
- of tracheal tubes pervading all 
the soft parts. These occasionally 
-jut dilatations, acting as reser- 
voirs — the foreshadowing of the 
cavities of the higher 
tribes. Of such, ', represent- 

ing the air- tracheal dilata- 

- of the Bcolia hortorum, is an 
Stratum. The tracheal tul 
Communicate with the external air 

* American Journal of Medical Science. May. 1838. 

urinations be continued ? What 
i' Bpiratioo ? How is this 
complishi 'I in the 1 >w< r aquatic animals? What is the type of 
I'iration in insei to? De* ribs the illustrations in Fig*, 59, 60. 




142 



APPEARANCE OF THE LUNG IN FISHES. 



through openings which may be obstructed by a valv- 
ular arrangement, as represented in Fig. 60. The pho- 

Fia. CO. 




Spiracle of insect 

tograph from which this figure was taken shows such a 
spiracle magnified 75 diameters. These organs may be 
seen arranged in rows on each side of the body, as in 
the common caterpillar. The mode of guarding the or- 
ifice varies in different cases, sometimes tufts of hair be- 
ing resorted to, and sometimes, as in the figure, valves. 
The true lung is first recognized in the swimming 
bladder of fishes as a simple sac. In the carp, the tend- 
ency to a multi-chambered construction already ap- 
pears under the form of two such bladders, a, 6, COm- 



F/tf. Gl. 



e; 




Air-sac of fish. 



municating with each other through a narrow tube. 
These are connected with the oesophagus, o, by means 
of the pipe c, c?, the fish being thus enabled to remove 

Under what circumstances does the true lung first appear ? 



RESPIRATION OF FISHES. 143 

at pleasure a part of the air contained in the sacs by 
muscular compression. Though this mechanism is a 
rudimentary lung, it does not properly subserve the 
duty of such an organ, but is employed for producing 
variations in the specific gravity of the animal by intro- 
duction or removal of air. In these tribes the gills are 
the mechanism for aeration. It is accomplished in the 
following manner : The mouth is periodically filled with 
water, which is driven past the gills by muscular com- 
pression, and thereby the carbonic acid is removed from 
the blood circulating in those organs, and oxygen is ob- 
tained in return. For this reason, a fish dies very quick- 
ly when its mouth is kept open. The angler knows that 
it is not owing to any loss of blood, nor to any injurious 
lesion that the hook may cause, but simply to suffoca- 
tion, the* water no longer lifting the gill covers, but mere- 
ly passing out through the open mouth. 

The experiments of Humboldt and Proven9al clearly 
demonstrate the analogy between aquatic and aerial res- 
pirations ; for water is not decomposed by the breathing 
of fishes : it is the air dissolved in it that is used. In the 
sample examined by these chemists, there was 20.3 per 
cent, of its volume of air, consisting of oxygen 29.8, ni- 
trogen 66.2, and carbonic acid 4.0, in the hundred parts. 
After the fishes had remained in it for a due time, it still 
contained 17.6 per cent, of its volume of air, but this in 
100 parts now consisted of oxygen 2.3, nitrogen 63.9, 
and carbonic acid 33.8. There had therefore been a 
consumption of oxygen and evolution of carbonic acid, 
together with a slight removal of nitrogen, this being 
the general result witnessed in aerial respiration. In a 
similar course of experiments on the breathing of gold 
fishes, made by myself, the result corresponds to the pre- 
ceding Btatement, only the water I used was richer in 
Oxygen gas, and the transposition into carbonic acid did 
not seem by any means to be so complete. I also re- 
marked the same diminution in the quantity of nitrogen, 
but am disposed to attribute it not so much to the con- 
sumption of that gas by the fishes as to its diffusion from 

What function does the swimming bladder of fishes disci 
II w is the respiration of fishes carried on? Why ig ir that a fish 
dies bo quickly on the hook? What i.s the constitution of the air 

contained in water ? 



144 



RESPIRATION OF REPTILES AND BIRDS. 




\] 



the water into the atmosphere, the solvent 
power having changed by the substitution 
of carbonic acid for oxygen. 
. In reptiles the lung presents the sac-like 
form, as in Fig. 62, a pulmonary artery 
passing on one side, and a pulmonary vein 
returning on the other : a is the trachea ; 
J, its bifurcation ; c, pulmonary artery ; d 
d, pulmonary vein. It often occurs that 
the two lungs are not equally developed, 
one of them, B, being rudimentary as com- 
pared with the other, A. Into such a sac 
in serpents the air is forced by muscular 
contraction, a kind of swallowing. It is 
expelled from them by the contraction of 
the abdominal muscles, and hence the hiss- 
ing sound emitted during its expulsion. 
From the simple sac to the cellular lung 
the advance is made by degrees, a devel- 
opment of parietal cells upon the inner sur- 
face taking place. At the intermediate 
stage betweeu the simple sac and the highly 
subdivided res- Fig ^ G3 

piratory organ 
of the mammals, 
the condition of 
things is well il- 
lustrated by the 
lungs of the frog. 
In Fig. 63, a is 
the hyoid appa- 
ratus ; #, cartilaginous ring at 
the root of the lungs; c, the 
pulmonary vessels ; and d d, 
the pulmonary sacs. 

Of all tribes, the respiratory 
mechanism is most highly de- 
veloped in birds, which, besides 
being provided with lungs, 
have air-sacs between the muscles, and respiratory mem- 
branes spread on the interior of the hollow bones. It 

What change does the breathing of fishes impress on it? How is 
the respiration of reptiles carried on ? Describe Fig. 63. 




Lung of reptile. 




Lungs of frog. 



THE LUNGS OF MAN. 145 

is in consequence of this that a bird is killed so readily, 
oven by a very small shot, since it is scarcely possible to 
make a perforation into any part of the body without 
opening the respiratory cavity. 

In man, the bronchial tube, as it passes into each lung, 
branches forth like a tree, the walls of the tubelets thus 
arising having cartilaginous rings to preserve their form 
under compression, circular organic muscular fibres to 
enable them to contract, and longitudinal fasces of elas- 
tic tissue to shorten them after extension. In their in- 
terior they are covered with mucous membrane provid- 
ed with cilia. When the proper degree of minuteness, 
about ^j of an inch, is reached, they consist alone of 
elastic membrane, interspersed with muscular fibres, and 
upon their sides the air-cells open ; sometimes single 
ones, or sometimes many cells communicating with one 
another, discharge through the same orifice, the tubelet 
itself ending in a cell. The air-cells have various dimen- 
sions, from -t^j- to yryVo °f au inch. Their structure is 
like that of the tubelet. The pulmonary capillaries are 
spread so closely upon them that the spaces between 
them are less than their own diameter, which, on an av- 
erage, is -3-0V0 of an inch. As the cells are close togeth- 
er, the blood-vessels passing between them are brought 
in communication with the air on both sides, and arte- 
rialization is thus rapidly and completely performed. 
Each tubelet, with the air-cells thus clustered upon it, 
i< a miniature representation of the lung of a reptile. 
The cells themselves communicate by lateral apertures 
with one another. The membrane lining their interior 
:iarply folded at the apertures, and there are reasons 
for supposing that it contains organic muscular fibres. 
It i< Stated that each terminal bronchus has nearly 
•00 air-cells clustered upon it, and that the total 
nuiii "> millions. 

mode of distribution of the air-tubes is represented 
in WigA 1 W). a is the larynx ; b 5, the trachea, 

the upper letter corresponding to the cricoid cartilage; e, 
the left bronchos ; d^tne right bronchus; <\j\ </, its ram- 

Whai u tb 90 easily killed by :i small shol ? I)<- 

e human long. What is the size of tin- sir-cella ? Bow 

the Uood-yesselfl bi a them? What u the estimated 

number of air-cell-? 

<■ 



146 



STRUCTURE OF THE LUNGS. 



Fig. 64. 




Human air-tubes. 



Fig. 05. 




The heart and lunj 



which it has to pass. 



ifications in the right 
]xm gJj/ h, ^rami- 
fications of the left 
bronchus in the left 
lung, Jc Jc. 

Fig. 65, arrange- 
ment of the heart 
and lungs, the latter 
in part section. 1, 
left auricle of the 
heart ; 2, right auri- 
cle; 3, left ventricle; 
4, right ventricle; 5, 
pulmonary artery ; 
6, aorta ; 7, superior 
vena cava; 8,innom- 
inata ; £, left primi- 
tive carotid ; 10, left 
subclavian ; 11, 12, 
upper rings of tra- 
chea and cartilages 
of the larynx; 13, 
upper lobe of right 
lung; 14, upper lobe 
of left lung ; 15, the 
right pulmonary ar- 
tery ; 16, 16, lower 
lobes of lungs. 

Fig. 66 illustrates 
the manner of dis- 
tribution of blood- 
vessels on the air- 
cells of the lungs. 

By the aid of this 
elaborately con- 
structed mechanism 
the air is brought 
to the blood. There 
;3> are three distinct 

stages through 
The first is the filling of the tra- 



Describe Figs. 64 and 65. 
troduction of the air ? 



How many stages are there in the in- 



.MOVEMENTS OF RESPIRATION. 



147 




Distribution of capillaries on air-cells of the lungs. 



ohea and larger 
ramifications of the 
bronchial tub< 
this is accomplish- 
ed by atmospheric 
pressure, brought 
into play by mus- 
cular contraction. 
The second stage is 
the translation of 
the fresh air from 
the larger bronchial 
tabes to the ulti- 
mate air-cells : this 
i-- accomplished on 
the principle of gaseous diffusion. The third stage is 
the passage from the air-cells, into the blood : this is 
through the wall of the cell, the wall of the blood-ves- 
sel, and the sac of the blood-disc; it involves passage 
through membranes, and implies their condensing ac- 
tion. Each of these three stages we have now to con- 
sider. 

1st. The introduction of fresh air into the trachea and 
larger ramifications of the bronchial tubes is accomplish- 
ed by muscular contraction, calling into operation atmos- 
pheric pressure. In tranquil respiration the diaphragm 
is nearly sufficient for this purpose. This muscle, form- 
ing the convex floor of the chest, as soon as it contracts, 
imes more nearly a plane figure, thereby increasing 
the content of that cavity; and, just as in a common 
9, when the lower board is depressed, the air flows 
in through the pipe, so, on the descent of the diaphragm, 
the air tlows in through the trachea, forced by the ex- 
ternal pressure. 

An experimental illustration ofthc manner in which the 

air [need into the cavity of the lungs by the de- 

•it ofthc floor of the chest, and then expelled by its ele- 

vati"D. i< represented in fflg.61 (p. l i^). a << is a tube 

- half an inch or more in diameter, and six or eight 

■ the lower end of it a bladder, ft, is tight- 
ly attached. The tube i- passed through the neck of a 



1> sci '■'■> ■ the : ' 



What i- the mode of action ofthc dia- 



148 



MOVEMENTS OF RESPIRATION. 



bell-jar, c c, air tight. A large 
glass reservoir of water, filled 
to the height d d, receives the 
bell-jar, as shown in the figure. 
When the jar is depressed in 
the water the air is expelled 
from the bladder, and when 
the jar is raised the air flows 
in. By alternately elevating 
and depressing the bell, the 
bladder executes movements 
like those of the lungs, of 
which, indeed, it is a repre- 
sentation ; the glass tube be- 
ing the trachea, the bell-jar the 
walls of the chest, and the ris- 
ing and falling water-level the 
rising and falling diaphragm. 
In this illustration the bladder 
is, of course, perfectly passive, 
as was at one time supposed 
to be the case with the lungs : 
an erroneous opinion, present- 
Mechanism of Respiration. \y to \y e corrected. 

In the mature period of life, and especially in deep 
respiration, the action of the diaphragm is insufficient 
for the introduction of air, and a still farther volume is 
obtained by raising the ribs, which increases the dimen- 
sions of the chest from right to left, and also from front 
to back. In men, this effect takes place more particu- 
larly through the movements of the lower ribs, and this 
form of respiration is therefore sometimes called the in- 
ferior-costal ; but in women the upper ribs are more 
movable, the dilatation of the chest is there greater, and 
the respiration therefore designated as the superior-cos- 
tal. In these movements of the ribs, and especially in 
violent respiration, many muscles are involved. 

In the reverse act, that is, in expiration, or the expul- 
sion of air through the trachea, the floor of the chest is 
raised. The diaphragm, when it contracted, made press- 

What does Fig. 67 illustrate? In deep respiration, what more is 
done? What difference is there between the respiration of men and 
women ? How is the expulsion of the air accomplished ? 




MOVEMENTS OF RESPIRATION, 149 

ore upon the viscera of the abdomen, and forced the 
muscular walls of that cavity outward; but, as soon as 
the diaphragm relaxes, the abdominal muscles contract, 
and thus an antagonizing force is originated tending to 
expel the air. In this the elasticity of the lungs and of 
the walls of the thorax itself affords a great assistance. 
Owing to this elasticity, the muscular exertion required 
for the introduction of the air greatly exceeds that re- 
quired for its expulsion. 

In tranquil respiration, we may regard the changing 
of the air to be accomplished by the alternate depres- 
i and elevation of the diaphragmatic floor of the 
chest. On an average, this takes place 17 times in a 
minute, and in an adult of the standard size we may as- 
sume that 17 cubic inches of air are introduced at each 
inspiration. One breath in five is usually deeper than 
the other four. The statement often made, that five 
pulsations correspond to one respiration, must be re- 
ceived with a certain restriction. In pneumonia, the 
respirations may be to the pulsations as 1 to 2 ; in ty- 
phoid fever, as 1 to 8 ; and even in a state of health 
there may be considerable variations. 

By muscular movements, thus calling into action at- 
mospheric pressure, the air is drawn, but not forced, into 
the respiratory apparatus. Considering, however, the 
contents of the lungs, which can not be taken at less than 

• cubic inches, it is clear that the amount is not more 

than sufficient to fill the nasnl passages, the trachea, and 

the larger ramifications of the bronchial tubes. Lying 

nearest to the outlet, it would be the first to be expelled 

by the act of expiration. There could be no exchange 

of the fresh for the foul air unless some additional means 

nployed for accomplishing its transference from 

Bjer ramifications of the bronchial tubes to the re- 

ir-cells. 

• nee of fresh air to the cells is accom- 
plished by resorting to two different principles, the dif- 
fusion offri into one another, and muscular con- 
traction. 

An estimate of the relative share taken by each of 

ity of the lun-_'< operate? Whafl i> the num- 
ber of respirations in a minute? How many cubic inches of air arc 

receiv 



150 EFFECT OF GASEOUS DIFFUSION. 

these is arrived at by an examination of the absolute ve- 
locity with which gases diffuse into one another. The 
statement that gases act as vacua to each other has led 
to some very erroneous conclusions. It has been taken 
for granted that the actual diffusion is very rapid, per- 
haps approaching to the velocity of gases rushing into 
a void. But I have shown* that this is altogether a 
misconception, and that the transit of fresh air from the 
bronchi, exchanging with foul air from the cells, if con- 
ducted on that principle alone', would require a period 
greatly beyond the time occupied for one respiratory 
act, about three seconds and a half. 

To an additional agent we must therefore look for a 
complete explanation, and this, I think, is presented in 
the circular organic fibres of the bronchial tubes and 
cells. It has long been understood that these possess 
the power of varying the capacity of the tubes. 

With this agency in view, this second stage of the 
process is accomplished as follows : The carbonic acid, 
vapor of water, and excess of nitrogen, if any, that have 
accumulated in the cells belonging to any given bron- 
chial tree, are expelled therefrom by the muscular con- 
traction of the circular organic fibres, and are delivered 
into the larger bronchial tubes, in which diffusion at 
once takes place with the air just introduced. As soon 
as the expiration is completed, relaxation of the muscu- 
lar fibres occurs, and the passages and cells dilating, 
both through their own elasticity and the exhaustive 
effect arising from the simultaneous contraction of other 
bronchial trees, fresh air is drawn into them, the alter- 
nate expulsion and introduction being accomplished by 
muscular contraction and elasticity, the different bron- 
chial trees coming into action at different periods of 
time, some being contracting while others are dilat- 
ing. 

3d. The third stage is the passage of oxygen from the 
cells to the blood : it is through the wall of the cell, the 
wall of the blood-vessel, and the sac of the blood-disc. 
The carbonic acid issues from the plasma, and passes 

* American Journal of Med. Sciences, April, 1852. 

At what rate does respiratory diffusion take place ? What is the 
action of the muscle fibres of the lungs ? Explain the third stage of 
respiration. 



\EKAL STATEMENT OF THE RESPIRATORY ACT. 151 

through the wall of the blood-vessel and the wall of the 
cell. 

Many physiologists have supposed that this exchange 
of oxygen for carbonic acid takes place on the principle 
of diffusion. On the authority of Valentin and Brun- 
ner, it has been asserted that the proportional exchange 
actually observed is 1174 of oxygen for 1000 of carbon- 
ic acid* these being the theoretical quantities under the 
law of diffusion ; but there is no difficulty in proving 
that this is a physical impossibility, for the exchange is 
not merely that of oxygen and carbonic acid ; it is much 
more complicated. The lungs regulate the quantity of 
free nitrogen in the system, and there is a constant es- 
cape of the vapor of water. These bodies, moreover, 
are not presented in the gaseous state, but in that of 
liquid solution, and the wall of the cell, of the pulmo- 
nary capillary, and of the blood-disc, by their condensing 
action, totally disturb the conditions of diffusion. 

EXrLAXATIOX OF RESPIRATION. 

The act of respiration in man is therefore accomplish- 
ed in the following way. The air, introduced by atmos- 
pheric pressure, brought into play by the action of the 
diaphragm and other respiratory muscles, fills the nasal 
passages, the trachea, and larger ramifications of the 
bronchial tubes. Between it and the gas coming from 
the pulmonary vesicles, diffusion steadily takes place, 
tending to remove the cell gas into the atmosphere; 
but this gas is not brought from the vesicles by diffu- 

] alone, which could not act with sufficient speed, 
but by the contraction of the circular organic muscles 
of the bronchial tubelets and of the cells, the different 
bronchial trees not acting simultaneously, but success- 
ively. A- soon as contraction is over, the tubes expand 
by their elasticity, and the air is drawn into the cells, 
each bronchial tree, by its contraction, aiding the expan- 
sion of the adjacent ones. The longs are therefore not 
altogether passive during respiration, as is sometimes 

I. The exchange between the gas in the cells and 
that in the blood does no1 take place through simple 
diffusion, or in quantities proportional to the diffusion 

Does the principle of simple diffusion here apply? Give a gener- 
al explanation of the respiratory pro 



152 VOLUME AND CHANGES OF THE GAS. 

volumes of oxygen and carbonic acid. It is a complex 
diffusion, disturbances arising from the gases in the 
blood being either dissolved or combined. The process 
ends by the expulsion of the foul air accumulated in the 
larger bronchi and trachea, by the diminution which 
takes place in the capacity of the chest during expira- 
tion, occasioned by the contraction of the expiratory 
muscles, the elasticity of the walls of the chest, and of 
the lungs themselves. 

Such is the arrangement by which fresh air is con- 
stantly presented to the blood, and the gases and vapors 
exhaling from it are removed. The degree of exhaus- 
tion occurring in the chest scarcely justifies the expres- 
sion sometimes used, " a tendency to a vacuum," since 
it is rarely more than competent to raise water a single 
inch. This may be readily proved by dipping a glass 
tube, open at both ends, and half an inch in diameter, 
into a cup of water, and placing the projecting extrem- 
ity between the lips, taking care to keep the muscles of 
the mouth at complete rest. It will then be seen that 
at each inspiration the water rises about an inch, and at 
each expiration is depressed to a similar extent. Its 
movements indicate the degree of rarefaction or com- 
pression occurring in the chest. 

The diurnal amount of air introduced into the lungs 
has been variously estimated from 226 to 399 cubic feet. 
A part, from 4 to 6 per cent., of the oxygen thus intro- 
duced disappears in the lungs, and the expired air is 
charged with from 3 to 5 per cent, of carbonic acid. 
But that nothing analogous to combustion occurs in 
those organs is proved by their temperature, which is 
not higher than that of other parts of the system. More- 
over, carbonic acid can be withdrawn from venous blood 
in a Toricellian vacuum, and still better by agitating the 
blood with such gases as hydrogen and nitrogen, prov- 
ing that the gas pre-exists in the venous blood before 
its entry into the lungs, and is not formed in those or- 
gans, unless, indeed, it exists as a bicarbonate, as already 
mentioned. The quantity of carbonic acid thus disen- 

What is the actual amount of rarefaction in the lungs? How 
may it be measured? What is the diurnal amount of air intro- 
duced ? How is it known that nothing like combustion occurs in 
respiration ? 



RATIO OF INSPIRED AND EXPIRED OXYGEN. 153 

gaged is less than the quantity of oxygen absorbed, be- 
cause much of the latter is consumed in the production 
sulphuric and phosphoric acids, which escape in the 
urinary secretion, as indeed does a large quantity of car- 
bonic acid itself. 

With respect to the ratio between the quantity of 
gen inspired and that contained in the expired car- 
bonic acid, a variation will be observed, depending on 
many conditions, as, for example, on the nature of the 

food. 

For the perfect oxidation of the different elements of 
food, very different quantities of oxygen are required ; 
thus, for the oxidation of 100 parts of fat, it would re- 
quire 202.14 of oxygen; for that of starch, 118.52; for 
that of muscle, 147.04. 

For reasons to be considered when we treat of the 
production of heat, the quantity of carbonic acid disen- 
gaged varies with external circumstances. When the 
weather is cold it is greater than when it is warm. 
Thus at 6S° there is twice as much liberated as at 106°. 
It increases during exercise and after eating, but dimin- 
ishes during sleep. More is set free by men than by 
women ; it also varies with age, the proportion rising 
from eight years to thirty, remaining stationary to forty, 
and then declining. It changes with the frequency of 
the respirations. The total quantity of carbon daily re- 
moved by respiration may be estimated at eight ounces. 

Besides the carbonic acid removed, a large quantity 
of water is excreted by the lungs, for the expired air 
may be regarded as saturated, or containing the maxi- 
mum quantity of water for 94°. For the vaporization 
<»f this water much heat is consumed, as is likewise the 
• for the warming of the introduced air, which, no 
matter what the externa] temperature may have been, 
IS 1 »r< -ULrlit to that of the ]in 

With r< the absolute amount of air expired, 

and also the quantity of water removed by the lui 

cperiments have been made by my Bon, Dr. J. C. 

Why is the qui arbonic acid leas than thai of oxygen in 

volume? What amount of oxj r gen i- required in the <•:!-<• of fat, 
h, and muscle, if i 1? What circumstances control 

the amount oi . aged ? How much carbon u daily re- 

mo v 

(; 2 



154 QUANTITY OF AIR AND WATER REMOVED. 

Draper ; the principle upon which they were conducted 
may be thus briefly stated. The air from the lungs, 
which has a dew-point of 94°, was passed by a wide 
tube through a metallic condenser kept at 32°, care be- 
ing taken to have as little obstruction as possible to its 
egress. The weight of the water collected in the con- 
denser furnished the means of calculating, by a simple 
formula, the quantity of air expired, for the vapor, leav- 
ing the respiratory passages at 94°, and that leaving the 
condenser at 32°, were at their maximum densities. 
Computations executed upon data obtained on this prin- 
ciple furnish the following, among other interesting re- 
sults : 

1. On making sixteen respirations in the minute, and 
continuing the experiment for twenty minutes, the av- 
erage of five different series of experiments gives 622 
cubic inches of air expired each minute. 

2. On making six respirations in a minute, and contin- 
uing the trial for twenty minutes, the average of three 
series of experiments gives 511 cubic inches for the air 
expired each minute. 

3. On making thirty- three respirations in a minute, 
and continuing the experiment for twenty minutes, the 
average amount of air is 1077 cubic inches for the air 
expired in each minute. 

On comparing these three statements, it appears that, 
the first representing normal, the second very slow, the 
third very quick respiration, the absolute amount of air 
removed from the lungs is directly proportional to the 
number of respiratory acts in a given period of time, 
and this notwithstanding such variations in the depth 
of the inspirations as under such circumstances are like- 
ly to occur. 

With respect to the quantity of water removed from 
the lungs, he also shows, 

4. That, at an atmospheric temperature of 55°, the 
dew-point being 49°, the number of expirations sixteen 
per minute, the quantity of water removed per minute 
is 4.416 grains. 

Give an account of the experimental results related in sections 1, 
2, 3. What is the effect in normal, slow, and quick respiration ? 
What is the quantity of water exhaled per minute, as shown in sec- 
tion 4 ? 



EFFECT OF RESPIRATION ON THE BLOOD. 155 

5. The other conditions remaining the same, but the 
respirations reduced to six per minute, the amount of 
water removed per minute is 3.586 grains. 

6. The other conditions remaining as before, but the 
number of respirations increased to thirty-three per 
minute, the amount of water removed j)er minute is 

1 grains. 

From these statements it therefore appears that the 
quantity of water removed from the blood by respira- 
tion increases with the frequency of the respiratory acts, 
and this notwithstanding variations which, under such 
circumstances, must take place in their depth. Theo- 
retically, it is also obvious that the absolute amount 
thus expired is dependent on the existing dew-point of 
the air. 

The time of exposure of the blood to the air is only 
a second or two. The color changes, as has been de- 
scribed before, from blue to crimson, and the tempera- 
ture rises a degree or two, as is shown by an examina- 
tion of the left cavities of the heart. The water thus 
removed is not pure, but contains animal matter in a 
state of decay. 

Though we have treated of the act of respiration as 
consisting of two separate and consecutive stages, inspi- 
ration and expiration, in reality it proceeds continuous- 
ly. At the respiratory surface, which is the w r all of the 
air-cell, the passage of oxygen inward, and of carbonic 
acid and steam outward, takes place in a steady and un- 
varying manner. 

The introduction of an irrespirable gas into the lungs, 
or the prevention of the access of the atmosphere, brings 
the circulation of the blood to a stop; for that move- 
ment depends, as I have shown, on the aeration taking 
place in the pulmonary capillaries. Tn such cases there 
will he an i tment of the right heart and vessels 

arising therefrom, hut, if the Btoppage has not lasted too 

long, the current may he re-established by re-establish- 
in:: the respiration. Death commonly ensues on an ex- 
elusion of the air for five minutes, and, in cases of drown- 

What is the quantity of water exhaled per minute, tfl Bhown in 
<1 how doc- it van? Fur what length oftime is 

the bl sir? \i respiration continuous or recipro- 

cating? What i> the effect oftfae introduction of irreepirablegaeee? 



156 NERVES OF RESPIRATION. 

ing, it is rare for restoration to be effected if the immer- 
sion has lasted more than four. 

In the respiration of protoxide of nitrogen, a gas 
which is an energetic supporter of combustion, and act- 
ing more powerfully on the animal system when re- 
spired than even oxygen itself, on account of its ready 
condensibility by pressure, or by membranes, and solu- 
bility in water, the circulation is greatly quickened at 
first, and a state of exhilaration ensues; but this is soon 
followed by a condition of depression, or even of coma, 
for the quantity of carbonic acid produced in the sys- 
tem is now so great that the lungs are wholly inade- 
quate to effect its removal, and all the symptoms of poi- 
soning by carbonic acid come on. 

The introduction of air into the system is, to a certain 
extent, automatic, and, to a certain extent, dependent on 
the will. In tranquil respiration we are wholly uncon- 
scious of the motion ; the exciting impression is made 
on the pneumogastric nerves, and, being conveyed to 
the respiratory ganglion, the medulla oblongata, is there 
so reflected that through the agency of the phrenic 
nerve motion takes place in the diaphragm. The auto- 
matic, and therefore unconscious movement, to a certain 
extent, occurs in that way. But there is no doubt that 
the brain also participates in the function. No other 
evidence of this is required than that we can " hold the 
breath," and the relative share that the voluntary and 
automatic mechanisms take is illustrated by the circum- 
stance that this holding of the breath can only be per- 
sisted in for a certain time, when the necessity for re- 
spiring becomes altogether uncontrollable. 

It is not, however, to be supposed that so important 
a condition as that of the introduction of the air is only 
slenderly provided for. Many other nerves, besides 
those mentioned, take part in it directly or indirectly ; 
the fifth pair, the nerves of the general surface, and also 
the great sympathetic, the intercostals, the spinal acces- 
sory, which probably gives its motor property to the 
pneumogastric. Opinion has differed respecting the 
cause which produces the necessary impression on the 

What of protoxide of nitrogen or oxygen ? To what extent is the 
introduction of air dependent on the will ? What are the nerves in- 
volved in respiration ? 



RESULTS OF RESPIRATION. 157 

receiving nerves, some referring it to the presence of 
venous blood in the capillaries of the lungs, and some 
to the carbonic acid in the cells. Moreover, there is 
reason to believe that the presence of an abnormal 
amount of venous blood in the respiratory ganglia will 
of itself give rise to respiratory movements through the 
proper centrifugal nerves. 

The control possessed fey the will over the introduc- 
tion of air stands in a close relation to the production 
of articulate or other sounds, and therefore to intercom- 
munication between individuals by speech. This in- 
volves not merely a general control alone, but also a 
particular one, reached by regulating the movements of 
the glottis by the agency of the superior and inferior 
laryngeal nerves. But though the will for these import- 
ant purposes exercises so marked a power of regulation, 
it is to be looked upon as superadded or incidental, and 
during sleep, coma, and that larger portion of life spent 
in total inattention to the carrying on of this function, 
it is discharged in a purely automatic way. 

The mechanism that accomplishes the surprising re- 
sults of respiration may therefore well challenge our ad- 
miration. As a self-acting or automatic contrivance, 
over which we have not a necessary control, it origin- 
ates in a single year nearly nine millions of separate mo- 
tions of breathing. It never fatigues us ; indeed, we 
are never conscious of its action. In the same time, a 
hundred thousand cubic feet of air have been introduced 
and expelled, and more than thirty-five hundred tons of 
blood have been aerated. In a future page we shall 
have to present the wonderful mechanism by which aeri- 
al currents, as they pass in and out of the respiratory 
apparatus, are incidentally employed as a means of pro- 
ducing musical notes or articulate sounds, and of thus 
iblishing a relation and communication between dif- 
ferent individuals. By these the feelings and thoughts 
are diffused, and in a mechanical origin commence those 
bonds which hold society together. 

How i> it thai the necessary impression is made on them? How 
arc the movements of the glottis regulated? Under what circum- 
stances is respiration purely automatic? How many respiratory 

movements are made in a year? In i lint time how much air lias 
l>een used, and how mnrh hlood aerated ? 



158 ANIMAL HEAT. 



CHAPTER X. 

OF ANIMAL HEAT. 

Participation of Organic Forms in external Variations 
of Temperature, — Mechanism for counterbalancing 
these Variations. — Development of Heat in Plants at 
Germination and Inflorescence. — Connection of Res- 
piration and Heat. — Temperature of Man. — His 
Power of Resistance. — The diurnal Variations of 
Heat. — Annual Variations of Heat. — Control over 
them by Food, Clothing, and Shelter. — Source of An- 
imal Heat. — Hibernation. — Starvation. — Artificial 
Reduction of Temperature by Blood-letting. — Prin- 
ciples of Reduction of Temperature.— *T1ieir Balance 
with the Heating Processes. — Local Variations elimi- 
nated by the Circidation. — Control by the Nervous 
System. — Rs Physical Nature. — Altotropism of Or- 
ganic Bodies. 

Owing to the earth's diurnal rotation on its axis, and 
its annual movement of translation round the sun in an 
orbit inclined to the equator, variations of temperature 
arise, the vicissitudes of summer and winter, day and 
night. 

In these variations all objects upon the surface of the 
planet participate ; organic forms are no exception. As 
the heat of the medium in which they live ascends or 
descends, theirs follows it at a rate dependent on their 
conductibility. 

Like mineral substances, the more lowly forms of life 
submit to these changes. They have no provision for 
check or compensation. In summer, the temperature 
of the stem of a tree rises without any restraint ; in 
winter it declines ; and, should the point be reached at 
which those nutritive changes that give motion to the 
sap cease, nothing is done to arrest the descent, and the 

Are organic forms affected by external variations of heat ? What 
is the consequence in the case of plants during winter ? 



COLD AND HOT BLOODED ANIMALS. 159 

whole organism passes into a slate of torpor, hyberna- 
tion, or temporary death. 

Now, since this following of atmospheric tempera- 
tures must take place in every organism as well as in 
every mineral body, the construction of one having a 
uniform mode of existence in all climates and all seasons 
implies a resort to some subsidiary mechanism, which, 
though it may not check, may yet compensate for these 
vicissitudes. Accordingly, so nearly is this equalization 
accomplished in the highly-developed tribes, and a stand- 
ard temperature so nearly attained for them, that many 
physiologists, misled by imperfect observations, have 
concluded that such living beings are emancipated by 
nature from the operation of physical laws: an errone- 
ous conclusion, for in them that action is only concealed. 

In different races, the mechanism by which these va- 
riations of atmospheric temperature are balanced acts 
with different degrees of perfection. On this a subdi- 
vision has been founded, and animals classified as the 
cold and hot blooded. "We are not, however, to attach 
much importance to such an arrangement : it is rather 
imaginary than founded on any real distinction. In 
man, the temperature is near 100°; in fishes, it is about 
that of the water in which they live. Insects, in their 
larva and pupa condition, are cold-blooded ; in their per- 
fect condition, hot. 

AVe have now to explain what physical principles are 
resorted to in solving the problem of maintaining an or- 
ic form at a constant temperature in a medium the 
heat of which is variable; and as we may reasonably 
anticipate that these principles are the same in every 
tribe of life, it will facilitate our investigations to com- 
aoe with the simplest cases first. 

re are two periods in the life of a plant during 
which it simulates the functions of an animal in main- 
taining a temperature higher than that of the surround- 
ing air. T . 1st, at the germination of 
the during the functional activity of the 

}< l»e laid together, as in the making 

What don of compensation in the 

ler animal animals divided? What 

the life of plants when they act like animal-? 



160 THE HEAT OF PLANTS. 

of malt, the operation being conducted at a gentle tem- 
perature, and with the access of atmospheric air, oxygen 
disappears, carbonic acid is set free, and the tempera- 
ture rises forty or fifty degrees. A process of oxidation 
must therefore have been carried into effect, and to it 
we trace the heat disengaged, for carbon can not pro- 
duce carbonic acid without a rise of temperature ensu- 
ing. The loss of weight exhibited by a seed is there- 
fore due to its loss of carbon, and the whole effect is ex- 
plained in the statement that atmospheric oxygen has 
united to a portion of carbon contained in the seed, pro- 
ducing carbonic acid gas and an evolution of heat. 

Again, during flowering, the same action is repeated. 
The flower removes from the surrounding air a portion 
of the oxygen it contains, and replaces it with carbonic 
acid, the temperature rising, as accurate experiments 
have proved, in absolute correspondence to the quantity 
of oxygen consumed. Nor is this elevation insignifi- 
cant. A mass of flowers has been observed to raise the 
thermometer from 66° to 121°. 

If thus the disengagement of warmth is the result of 
oxidation, it must depend on the presence of air, and be 
regulated by the rapidity with which oxygen can be 
supplied. As we pass from the consideration of plants 
to that of animals, we discover that the production of 
heat must be connected with the power of the respira- 
tory apparatus, for it is through its agency that air is 
introduced. Extensive observation accordingly estab- 
lishes a close correspondence in each animal tribe be- 
tween the quantity of heat produced and the capability 
of respiratory apparatus. The lower tribes breathe 
slowly and are cold. Earthworms are only a degree or 
two warmer than the ground ; and even among verte- 
brates, fishes are only two or three degrees warmer 
than the water, a lowness of temperature in a great 
measure depending on the high cooling agencies that 
water exerts, its specific heat, and the facility with 
which currents are established in it. However, even in 
these cases the production of heat depends on the pow- 
er of the respiratory engine. The bonito can keep its 

Describe the effect during germination. Describe that during in- 
florescence. On what does the disengagement of heat depend ? 
Give examples of the temperature of the lower animals. 



CONNECTION OF RESPIRATION AND HEAT. 1G1 

heat 20° above that of the sen, and the narwhal main- 
tains a steady temperature at 96°. 

The organic operations involved in nutrition, and also 
the retrograde changes of decay, can only go on at their 
accustomed rates so long as standard limits of tempera- 
ture are observed. The proper progress of the actions 
of life implies a corresponding adjustment of heat, and 
this irrespective of the mere size of the animal. Even 
those that are microscopic must come under this rule. 
When the temperature of a liquid containing infusorials 
is caused to descend to the freezing point gradually, the 
last portions that solidify are those surrounding each 
of these little forms; a drop is kept liquid by the heat 
they disengage. In the same individual, the absolute 
temperature will depend on its respiratory condition ; 
thus insects, in passing through each of their stages of 
metamorphosis, present a definite condition as to their 
heat : the larva of the bee may be only two degrees 
above the air, while the perfect insect is 10°. What- 
ever accelerates the introduction and expulsion of the 
air, increases the warmth ; so a bee shaken in a bottle, 
and kept in a state of constant muscular exertion, will 
raise the temperature contained therein far higher than 
if he remains inactive. Among insects, those having the 
largest organs of respiration have always the highest 
temperature ; and, since muscular motion implies de- 
struction of muscular tissue by oxidation, and therefore 
development of heat, we should expect to find, as is act- 
ually the case, that animals possessing the highest pow- 

a of locomotion will possess also the highest temper- 
ature. Of all, therefore, birds, the endurance and en- 
v of whose powers of flight result from the perfec- 
tion of their respiratory mechanism, have the highest 
temperature. It is about 110°. Yet even here there 
. the sluggish ba'rn-door fowl has not the 
heat of the energetic swallow. 

ndard temperature of man is usually stated to 
08°, but from this mean it ranges within certain lim- 

upward and down. Muofa depends on the state of 

the health: of . every thing on the respiration. 

In fevers it will rise to 105°J in tetanus it may reach 

What i- t<» be remarked in I f infusorials? Bow n it 

among insects and birdfl ? What is the temperature of man ? 



162 VAKIATIONS OF HEAT IN THE HUMAN SYSTEM. 

110° ; the contrary in asthma, when it may sink to 82°, 
owing to imperfect access of air ; in cyanosis to 77°, ow- 
ing to imperfect aeration of the blood ; in Asiatic chol- 
era to 75°, owing to the non-reception of oxygen by the 
discs in their diseased state. It also varies with the pe- 
riod of life : in the new-born infant it is 100° ; it pres- 
ently sinks to 99°, and rises during childhood to 102°. 
Mental exercise in the adult increases it, bodily exertion 
still more. The special degree varies with the point on 
which the observation is made : the limbs are colder 
than the trunk, and this is the more marked as the point 
is more remote. On the leg the temperature may be 
93° ; on the sole of the foot, 90° ; while that of the vis- 
cera is 101°. 

In his residence in different climates, man is exposed 
to variations of temperature extending over a scale of 
200°. Toward the poles the cold of winter is often 
— 60° ; in the tropics the heat of summer +130°. For 
a short period his power of resistance is greatly beyond 
what these numbers would indicate ; he can enter with 
impunity an oven heated to 600°, provided the air is 
dry. In these cases, though excessive evaporation from 
the skin moderates the effect and keeps it within bounds, 
there is always a marked rise of temperature of the whole 
body. In a corresponding manner, exposure to cold pro- 
duces depression. 

Among these variations there is one class calling for 
critical attention. It is the diurnal variation ; less mark- 
ed in man, who instinctively makes provision against it, 
but well shown in the case of fasting animals. This il- 
lustrates, in an interesting manner, the controlling influ- 
ence of external conditions ; for if exposure to a high 
temperature, as that of an oven, compels a rise of the 
heat of the whole body, in spite of the conservative ar- 
rangements, and exposure to extreme cold compels a de- 
scent, we ought to expect that exposure to more mod- 
erate degrees would, in like manner, produce an impres- 
sion. 

The old astrologers were therefore not altogether 
wrong when they affirmed the doctrine of planetary in- 

How may it vary in disease ? What is the effect in different cli- 
mates ? How is it in artificial extremes of temperature ? Do the 
diurnal variations of heat affect man ? 



CALORIFIC INFLUENCE OF FOOD. 163 

fluences. The diurnal temperatures of a locality, as de- 
pendent on the position of the sun, are exhibited in the 

stem of man. The minimum of heat for the night, 
and the maximum for the day, find a correspondence in 
the decline of animal temperature at the former, and its 
at the latter period. Experiments on birds sub- 
mitted to absolute starvation show that, though in their 
normal state, at the commencement, the variation be- 
tween midnight and noon was only l£°, it gradually in- 
creased to 3 , until at last, the generation of heat whol- 
ly ceasing, the temperature gave way rapidly just pre- 
viously to death. 

If, therefore, it were possible for life to continue with- 
out the evolution of animal heat, it would be with the 
body as it is with the stem of a tree. It would follow 
the thermometric variations in the air, the maxima of 
heat and cold being somewhat later than the aerial ones, 
and within narrower limits, by reason of the low con- 
ducting power. The nearest approach to this is in cases 
of absolute starvation, and though in man the effect is 
masked by the due taking of food, it none the less ex- 

3. In human communities there is some reason be- 
yond mere custom which has led to the mode of distrib- 
uting the daily meals. A savage may dispatch his glut- 
tonous repast, and then starve for want of food ; but the 
more dedicate constitution of the civilized man demands 
a perfect adjustment of the supply to the wants of the 

item, and that not only as respects the kind, but also 
the time. It seems to be against our instinct to com- 
mence the morning witli a heavy meal. We break fast, 
kificantly termed, but we do no more, post- 

ling the taking of the chief supply until dinner, at 

middle or after part of the day. If men were only 

s of economy of time saved for the pur- 

if, on thi >n, they put in prac- 

m so many others, of never 

tifioation of their desires, the first af- 
fair of the morning would have been an abundant re- 
bifl something within us revolts, and 
that in all cl iboring, the intellectual, the idle. 

their heal ? 
What is the effect of food in the adjustment of temperature? Why 

li^ht meal taken in the morning? 



164 ANNUAL, VAKIATIONS OF HEAT. 

I think there are many reasons for supposing, when we 
recall the time that must elapse between the taking of 
food and the completion of respiratory digestion, that 
this distribution of meals is not so much a matter of 
custom as an instinctive preparation for the systemic 
rise and fall of temperature attending on the maxima 
and minima of daily heat. The light breakfast has a 
preparatory reference to noonday, the solid dinner to 
midnight. 

Once more I would remark, that we must not be de- 
ceived by the masked aspect the system in this matter 
presents. Its diurnal variations are concealed by agen- 
cies brought specially into operation for that purpose, 
but they exist in the physical necessities of the case ; 
and herein, I believe, we have a first glimpse of the 
cause of those periodicities, remarked by physicians 
from the earliest times ; for, though the nervous sys- 
tem, both in a state of health and disease, may seem to 
be their origin, it is not impossible that its changes are 
connected with variations thus taking place in the ex- 
ternal world. 

We have next to consider the effect of the annual va- 
riations of temperature, which reach their maximum 
soon after mid-summer and their minimum soon after 
mid-winter, the manner in which the system comports 
itself under them, and the means which instinct and ex- 
perience teach us to employ in providing against them. 

These annual variations of external temperature are 
chiefly combated by food, clothing, and shelter. The 
dietetic changes w r e make between winter and summer 
are founded upon the principle of using more combusti- 
ble food for the former, and less combustible for the lat- 
ter season : and, since the calorific effect of an article of 
food greatly depends on the quantity of oxidizable hy- 
drogen it contains, the winter diet has more of that ele- 
ment than the summer. Partly thus by varying the na- 
ture, and partly by varying the quantity of the food, we 
can effect a compensation to a certain extent. 

Of the manner in which the diet-compensation is aid- 
ed by variations in clothing little needs to be said. The 
experiments of Count Rumford established the fact that 

To what source may the periodicities of the body be traced ? How 
are annual variations of temperature accounted for? 



IMPERFECTIONS OF SHELTER. 165 

the conductibility of summer clothing is greater than 
that of winter, and therefore its resistance to the escape 
of heat is loss. It is sufficient merely to allude to the 
control gained by difference of thickness in the gar- 
ments, and by their amount or quantity. We instinct- 
ively make these adjustments to meet the existing exi- 
gencies, and, as far as may be, in this manner aim at a 
medium effect. 

The chuck upon external temperature by the use of 
clothing was doubtless one of the first contrivances of 
the human race. Even of savage life it is a cardinal 
feature. The check by adjustment of diet belongs to a 
civilized state, since it implies a certain control over the 
animal appetite and personal self-denial. Though great 
improvements in both of these will doubtless hereafter 
be made, when the principles of their operation are more 
generally and better understood, they must, even in 
their present condition, be regarded as having reached 
a higher perfection than the check by resorting to shel- 
ter. The art of constructing dwelling-houses may be 
said to be still in its infancy in all parts of the world, 
and yet in no particular is the physical condition of fe- 
males and children, and especially of the sick, more near- 
ly touched. It is only in our own times that attention 
has been drawn to the proper methods for the admission 
of warmth, and air, and light; the hygienic influences 
of furniture and decoration are unknown, beyond, per- 
haps a popular impression that it is unhealthy to be in 
a recently-painted apartment, inexpedient to sleep in a 
chamber where there are flowers, and unpleasant in 
summer to have a carpet on the floor, because it looks 
warm, and is thought to generate dust. The owner of 
a p:ilace, on which wealth lias been fruitlessly lavished, 
finds, on a cold day, that he can not obtain from his par- 
lor fire the necessary warmth unless by alternately turn- 

\ round and round. The testy valetudinarian sits in 
tir, tormented by drafts coming in from ev- 
ery quarter. In his vain attempts to stop the offending 

i him that his chimney is a 
great exhausting machine, drawing the air out of the 

What is tho conclusion drawn from Romford's experiments <>n 
clothing? What if d attained in compensa- 

tions of animal heat by 



166 ARTIFICIAL WARMTH. 

room, and that his means of warming and ventilation 
are the most miserable that could be resorted to, since 
radiation can warm only one side of a thing at a time, 
and fresh air under those conditions can only be intro- 
duced by drafts. 

To warm rooms by contrivances such as the open fire- 
place or stove is obviously unphilosophical, since the ef- 
fect of these is to exhaust the air of the apartment. The 
modern method of warming by furnaces, which act by 
throwing air duly moistened and of the right tempera- 
ture into the rooms, and therefore by condensation, is 
clearly a better system, since it not only puts an end to 
all drafts, the tendency being to force air out through 
every crevice instead of drawing it in, but it possesses 
the inappreciable advantages of giving uniformity of 
warmth, a perfect control over the degree of heat, and 
likewise over the nature of the air, which need not be 
drawn from the cellar, or the contaminated impurity of 
the street, but by suitable flues from the free and clear 
air above. Ventilating contrivances to force a supply 
of artificially cooled air in the summer, and warm air in 
the winter, into dwelling-houses, are still a great desid- 
eratum. 

By the aid of diet, clothing, and shelter, we are able to 
effect an almost complete compensation for the changes 
of diurnal and annual temperatures, and even to occupy 
any climate of the globe. It is the management of calo- 
ric that makes man what he is, and constitutes his spe- 
cial prerogative ; his degree of skill therein is the meas- 
ure of his civilization. The distribution of plants and 
animals, or, rather, their limitation within fixed bounda- 
ries, depends on the distribution of heat, but from these 
restraints man is free, because he can control tempera- 
tures. 

From these considerations of the effect of external 
heat on the human mechanism, we return to a more crit- 
ical examination of the modes by which heat is gener- 
ated, and its degree regulated in the body. 

In every instance we assert that the production of an- 
imal heat is due to oxidation taking place in the econ- 

What is the best system of warming dwellings yet introduced ? In 
what respects is it very imperfect? Do any other animals partici- 
pate with man in the power of controlling heat? 



EFFECT OF COMBUSTIBLE ALIMENT. 167 

omy, and giving rise to carbonic acid, water, and other 
collateral products. 

Reduced to its ultimate conditions, the evolution of 
animal heat depends on the reaction taking place be- 
tween the air introduced by respiration and the food, 
and as either one or other of these is touched, the result 
may be predicted. If, for example, into the digestive 
canal alcoholic preparations be introduced, they are ab- 
- -n of their liquid condition and divisi- 
bility, with readiness. The combustibility of alcohol, 
and the amount of heat it yields, are so great, that the 
primary effect of the oxidation is a warmth or feverish 
sensation. By reason of the changes now taking place 
so actively in it, the blood circulates with unwonted ra- 
pidity, and the supply to the brain increasing, that organ 
exhibits an unusual functional activity. IJut this dis- 
play of intellection is only temporary, and an opposite 
condition soon comes on, for, more carbonic acid accu- 
mulating in the blood than the lungs can get rid of, the 
depressing effects of that body commence, and eventual- 
ly the symptoms of poisoning by it ensue. 

Xot unlike this is the train of effects arising when, in- 
stead of varying the nature of the article ingested, we 
vary that of the gas respired. An energetic supporter 
of combustion, like the protoxide of nitrogen, gives rise 
to a feverish glow, cerebral activity, to be followed 
eventually by a deep depression, the poisonous influence 
of the carbonic acid produced being exhibited. After a 
while tl m casts it off, and recovers its condition 

of health completely. If there be an abstinence from 
food, since the introduction of air by respiration goes 
on without abatement, the body itself must trad* 

light, and emaciation occur. Its ten den- 
to follow the diurnal variations of temperature be- 
comes more and more strikingly marked as the proa 
Starvati< D, and finally a rapid and unchecked 

Yet even then life may 

1 by the application of sufficient external 

warmth, and from an extreme condition of attenuation 

an animal may be rescued by the vu od; bat for 

rtible aliment ? What of more 

vrbal ltc on th 



# 



168 EFFECT OF RAREFIED AIR. 

such a recovery the external warmth must be continued 
until there has been time for digestion and absorption 
to take place. If, however, such an extraneous aid be 
not duly applied, the temperature of the starving animal 
goes on diminishing, and he dies of cold. 

The doctrine we are here inculcating, that animal 
heat is due to oxidation in the system, is still farther 
strikingly illustrated by what might be termed starving 
the respiration. As cold is felt from want of food, so 
also it is from want of air. In ascending high mount- 
ains, the effect upon the system has been graphically ex- 
pressed as "a cold to the marrow of the bones;" a dif- 
ficulty of making muscular exertion is experienced; the 
strongest man can scarcely take a few steps without 
resting ; the operations of the brain are interfered with ; 
there is a propensity to sleep. The explanation of all 
this is very clear. In the accustomed volume of air re- 
ceived at each inspiration there is a less quantity of oxy- 
gen in proportion as the altitude gained is higher. Fires 
can scarce be made to burn on such mountain-tops ; the 
air is too thin and rare to support them ; and so those 
combustions, which should go on at a measured rate in 
the interior of the body, are greatly reduced in intensi- 
ty, and hence the sense of a penetrating cold. Such 
journeys, moreover, illustrate how completely the action 
of the muscular system, and also of the brain, is depend- 
ent on the introduction of air ; and under the opposite 
. condition of things, where men descend in diving-bells, 
though surrounded by the chilly influences of the water, 
they experience no corresponding sensation of cold, be- 
cause they are breathing a compressed and condensed 
atmosphere. 

The respiratory apparatus of certain animals permits 
a reduction in the amount of air introduced under expo- 
sure to a due degree of cold. Such animals are said to 
hibernate. At the coming on of winter their adipose 
tissues are engorged with fat. As they pass into their 
annual sleep, the rate of their respiration falls. The 
marmot, which in activity will make 140 respirations in 
a minute, makes now but 3 or 4 ; the temperature of the 
body descends, and combustion of the store of fat goes 

What are the physiological consequences of breathing a very rare- 
fied air ? What phenomena are displayed by hibernating animals ? 



COOLING AGENCIES. 109 

on more slowly. Yet it docs go on, for, toward spring, 
the animal has become very lean; sufficient heat is dis- 
engaged to permit the blood slowly to circulate, and so 
barely to keep up the functions of life. If, however, the 
■k of material available for combustion is insufficient, 
the animal dies. 

Although we can not interfere with the rate of respi- 
ration, we can affect the quantity of air introduced into 
the system by artificial means, as in the operation of 
blood-letting; for though, after blood has been drawn, 
we may make the normal number of respirations, 17 in 
a minute, and for each introduce 17 cubic inches of air, 
we have diminished the number of discs, the carriers of 
oxygen ; and, as the experience of physicians in all times 
has shown, there is no method so effectual in reducing 
any unusual or febrile temperature. So, in like manner, 
in Asiatic cholera, the marble coldness the body pre- 
sents is attributable to the loss of function of the discs, 
and the consequent abatement in the quantity of oxygen 
introduced. 

Thus far we have considered the means the animal 
mechanism possesses for raising its own temperature; 
it remains to show how it can also regulate it. For 
any thing that has thus far been said to the contrary, 
the combustions or oxidations continually going forward 
should establish a constant rise, and there must there- 
fore be some principle of restraining such a rise within 
due bounds. Considering also the incessant vicissitudes 
of atmospheric temperature, a constant degree could not 
be maintained unless the system possessecf the means of 
depressing as well as elevating its heat. 

That the means of regulating the heat are purely 

physical, we should expect for many very obvious rea- 

i oiiiy of heat is accomplished by non-condact- 

_ material. On this principle, hair, wool, and feathers 

lading the contact of the atmosphere, their 

ftibillty being brought into operation. In 

mail . the manner in which this is done is clearly 

intentional. Thus the down placed on the breast of a 
water-fowl is t<° off the chilling influence of the 

;.- interfering with the circula- 
tion? In what manner does 1 tion of blood act? Mention 

ii 



170 COOLING AGENCIES. 

water, which is there chiefly felt as the bird swims on 
the surface. The deposits of fat in whales, their blub- 
ber, at once affords a protection through its imperfect 
conductibility, and is also a store of combustible mate- 
rial for the purpose of respiration. 

The chief cooling agencies in anhrfals are, 1st. Radia- 
tion; 2d. Loss of heat by warming the expired air; 3d. 
Loss by contact of the cold external air; 4th. Evapora- 
tion. The circulation of the blood tends to establish an 
interior equalization, so that local variations are soon 
obliterated ; for, through whatever part the blood may 
flow, it attains the temperature thereof, and, passing in 
succession from part to part, equalizes the heat of all. 

It would be useless to offer any proof that a living 
being, like an inorganic mass, loses or gains heat, as the 
case may be, by radiation. Since, however, in man, the 
temperature is usually higher than that of the surround- 
ing medium, the result of this action is that cooling 
takes place. With regard to loss of heat by warming 
the expired air, it may be observed that, whatever the 
temperature of the external air may be, it is raised to 
that of the lungs after it has been brought into the res- 
piratory passages. This constitutes, therefore, a cooling 
agency of variable power, for the loss will be greater as 
the external heat is lower: if the atmospheric tempera- 
ture rose to 98°, loss in this manner would cease. Re- 
calling what has been said respecting the mode in which 
air is introduced, it is plain that this loss will chiefly fall 
upon the nasal passages, the trachea, and larger ramifi- 
cations of the bronchial tubes ; for, by the time the vol- 
ume inspired has made its way beyond that limit, its 
temperature must be nearly that of the body. The con- 
tact of the cold surrounding air, and more particularly 
of currents occurring in it, act chiefly upon the skin, and 
it is in preventing this loss that clothing becomes so ef- 
ficient. The difference we so frequently notice between 
the indications of the thermometer and our own sensa- 
tions are, for the most part, dependent on these currents. 
A temperature of 50° below zero can be sustained with- 
out much inconvenience if the air is perfectly calm, but 
not so if .there is any wind. Of all the cooling agencies, 

What are the chief cooling agencies ? How is it that heat is lost 
by radiation and contact ? 



COOLING AGENCIES. 1 71 

novation is, however, by far the most energetic. 
From the skin and the air cavities, large quantities of 
the vapor of water are exhaled. As the external heat 

-, the sudoriparous tubes act with increased energy, 
and poor out their excretion as drops of sweat faster 
than it can be removed. Their length has been esti- 
mated at 28 miles. Since, at the temperature of the 

ly, the heat of elasticity of the vapor of water is 
1114°, this continued vaporization from the skin and 
lungs is one of the most powerful sources of refrigera- 
tion. 

1 1 may be well to direct a closer attention to the spe- 
cial action of the air passages and skin as concerned in 
these cooling processes. The diurnal loss of water, by 
both organs conjointly, is usually estimated at 3^ lbs., 
of which the pulmonary exhalation constitutes about 
one thy\I, and the cutaneous about two thirds. The 
skin acts in a variable manner, losing more or less wa- 
ter as the external air is dryer or more damp. The re- 
moval of water therefore becomes a complex operation, 
in which three different organs are concerned — the skin, 
the lungs, and the kidneys. Of these, the skin acts me- 
teorologically and variably, as has been just remarked, 
and the respiratory organs for the most part uniformly. 
But since it is requisite, in the normal operations of the 

•em, that the diurnal average of water should be re- 
moved, the variable action of the skin throws a variable 
action upon the kidneys, for the excess that the skin 
can not evaporate must be strained off by these organs. 
In this regard the kidneys act, therefore, vicariously for 
the skin : and in hot weather, when the cutaneous losses 
are bat little urine is discharged; but in cold 

liner, when the cutaneous loss is diminished, its quan- 

I think, however, that as regards the respiratory or- 

gm ion should be made in their mode of ac- 

). In reality, tiny operate in a double way. 1st. 

Th( the nasal passage!, the trachea, and 

:<»n< of the bronchial tubes are oonoerned, 

• effectual ? What fa the 
I be the Action of the >kin. 

action <.t't!i<- kidneys? How fa it 
that the r organs operate in t: I in a doable way? 



172 BALANCE BETWEEN HEATING AND COOLING, 

meteorologically, and therefore variably, for the intro- 
duced air possesses the existing atmospheric tempera- 
ture ; is at one time warm, and at another cold ; yet, since 
it always leaves these passages at 94°, it removes from 
their surfaces sometimes less and sometimes more heat ; 
but it is not so with the action going on in the air-cells, 
the temperature of which, and of the air they contain, is 
always uniform ; and as water vaporizes into them, it 
must always do it at a uniform rate, and remove as its 
caloric of elasticity a uniform amount of heat. I there- 
fore decompose the loss of heat by the respiratory or- 
gans into two portions : one, which is constant, and tak- 
ing place in the cells ; the other, variable, occurring in 
the large air-ways, and, being meteorological, coincides 
in this respect with the cutaneous loss. In considering 
the diseases of the respiratory organs, it is well to keep 
this distinction in mind. m 

The establishment of the equilibrium of temperature 
in an animal is effected by the mutual operation of the 
heating and cooling arrangements. More or less heat, 
as the system requires, may be furnished by promoting 
or retarding the oxidation of respiratory material ; and 
since a living being, like an inorganic mass, is subject to 
e^ery external influence, its temperature tending to rise 
or fall, as diurnal, or annual, or seasonal changes may be, 
these, as well as its own interior variations, are held in 
check by the cooling or warming powers it can exert. 
Local differences within itself are eliminated in an indi- 
rect, but still very effectual manner, by the circulation 
of the blood; and, considering the range of variation to 
which it is exposed, and the frequency of the changes, 
the required equilibrium is admirably secured. 

I have reserved for a more special and prominent con- 
sideration the influence exerted by the nervous system 
over animal heat, since it is upon this that many have 
been disposed to deny the great truth that the heat of 
the body arises from oxidation. They say that it is 
produced by the nerves. Even a mental emotion gives 
rise to disturbance of temperature, and the face may be 
covered with blushes. Moreover, as experiments have 
proved, on cutting a nerve the temperature of the parts 

How is it that the balance of temperature is attained ? Has the 
nervous system any control ? 



1XFLI KNCE OF THE NERVOUS SYSTEM. 173 

it supplies declines ; on injuring the great nerve centres 
the temperature of the whole system lowers, even though 
artificial respiration maybe kept up. In cases of paral- 
ysis, the temperature of the disabled part may be very 
much lower than that of the sound. A paralyzed arm 
has shown a surface beat of 70° only, while the sound 
one has been at 92°. It is also said of decapitated ani- 
mals that they cool quicker when artificial respiration is 
kept up than when they are let alone. 

All this may be very true, yet it is very far from prov- 
ing that the nerves are the generators of animal heat. 
The engineer of a locomotive can regulate the speed of 
his train and control the production of steam by throw- 
ing more or less fuel on the fire, or by supplying it with 
more or less air ; but does any one impute the produc- 
tion of the heat to him ? If an accident should throw 
him off, thereby establishing a sort of analogy between 
his machine and the decapitated animals we have refer- 
red to, the stoppage that would soon ensue, and the dy- 
ing out of the fire, would by no means prove that he 
made the heat ! 

And so with the nervous system, its function is not a 
generative, but a controlling one. It determines in what 
way the combustive or oxidizing actions shall go on, but 
that is a totally different affair from forming the heat. 

Before specifying more particularly the views I enter- 
tain on this subject, I will remark, that the most super- 
ficial consideration satisfies us that oxidation in the sys- 
tem goes on in a regulated way. There is not an indis- 
criminate attack made by the arterial blood on whatever 
ifl next before it, but those particles only are removed 
which the needs of the system require. This therefore 
im] 16 overriding or superintending agency, that 

ie atom from destruction and surrender an- 
rtion assaulted may, to all appearanc 
tical in physical aspect and chemical constitution 
with an adj.. • that is passed by. There seem- to 

suspension of affinity in one case, and its 
>n in the other. 

Th( '-known facts in natural philoso- 

phy which throw a flood oflighl on this obscurity. If 

What \ U the function of the 

ner. rolling? 



174 ALLOTROPISM OF ORGANIC BODIES. 

a piece of pure zinc be placed in a glass of acidulated 
water beside a piece of copper, so long as the metals are 
kept apart no action whatever ensues ; but if a conduct- 
ing thread is laid from one to the other, the zinc instant- 
ly begins to oxidize, clouds of hydrogen gas bubbles rise 
from the copper, and the thread becomes at once red- 
hot and magnetic. On lifting the communicating thread 
all these actions cease ; on restoring it they instantly re- 
cur. We think we explain them by saying that they 
are all due to the decomposition of water by the zinc. 
But why was the zinc passive when alone, and why did 
it assume this activity when merely touched by another 
metal ? Does not all this serve to show that substances 
may be, as it were, in a quiescent state, and on the ap- 
plication of what may perhaps seem the most insignifi- 
cant cause, may suddenly assume activity, and forthwith 
satisfy their chemical affinities ? There is nothing in the 
graduated oxidations going on in the system more ob- 
scure or more unaccountable than the phenomena of a 
simple Voltaic circle. Their effects are almost parallel. 

All elementary substances appear to have the quality 
of assuming active and passive conditions. Carbon, 
moreover, presents many intermediate forms. As dia- 
mond it is extremely incombustible, and. is set on fire 
with difficulty even in oxygen gas ; as lampblack it will 
kindle spontaneously. With these differences in its re- 
lations with oxygen, it also exhibits great variations in 
its optical, calorific, mechanical, and other properties. 
These transitions of state may be induced by various 
causes, especially by the agency of what are called the 
imponderable principles, as by rise of temperature, and 
exposure to the sun-light. Thus, in the case of chlo- 
rine, I have shown that, though it refuses to combine 
with hydrogen so long as it is in the dark, an exposure 
to indigo-colored light will cause it to unite with ex- 
plosive energy with that substance ; and these pecul- 
iarities are retained by bodies when they go into union 
with each other. 

The properties here spoken of have been designated 
■ * ■— ■ 

How may the controlling action of the nervous system be illus- 
trated by electrical experiment? Give an example of the active and 
passive forms of bodies. How may these transitions of form be ac- 
complished ? 



OF SECRETION. 175 

by Berzeliu8 as the allotropism of bodies. I have en- 
deavored to prove that allotropism is the true cause of 
many of the obscure facts we meet with in the animal 
mechanism ; for it is very clear that something so mod- 
ifies the relations of the tissues to oxygen that they are 
not indiscriminately destroyed by it, but these parts 
yield id a measured or regulated way ; and since, in in- 

ganio substances, the influence of the imponderables 
can compel the assumption of an active or passive state, 
there is nothing contradictory in imputing to the nerv- 
system a similar power. 

In this manner we may therefore conclude that, so far 
as tissue destruction is concerned, the nervous system 
possesses a governing or controlling power ; that by 
keeping parts in states answering to the passive and 
active conditions of inorganic chemistry, it can suspend 
the action of the respired oxygen or permit it to take 
e fleet. 



CHAPTER XI. 

OF SECRETION. 

SEROUS, MUCOUS, AXD HEPATIC SECRETIOlSfe. 

Object of Secretion. — Type of secreting Mechanism. — 
tiltration <ni<l Cell Action. — Of Serous Membranes 
(tn<l their Secretions. — Of Mucous Membranes end 
their Secretions. — The Liver: its Development and 
Structure. — Source^ Quantity, Composition, Uses, and 
]• late <>j' th i 11 ih . — Eeistei / ce of b Wary Ingn < lii n t* 
in th Blood.— Production of Sugar and Fat in th 
IAver. — Changes of the Blood-cells in it. — Gem ral 
mary of th fourfold Action of th Liver: it 
S /;/,//• and FlU, eliminates Bile, is t/ /( Seat 
of the Anal Destruction of old BloodceUs^ and of the 
Completion of new Ones. — Qftht du <>/<</tds. — 
Th Fundi* 

Tw g of substances occur in the blood — the 

decay and the elements of nutrition. The 

What tion li:i- b mcb states? What mny 

finally be conch action of the neirou 



176 FILTRATION AND CELL ACTION. 

equilibrium of the system requires that the former should 
be removed and the latter appropriated. 

The primary object of the function of secretion is this 
dismissal and appropriation, and therefore, through the 
latter duty, secretion becomes connected with nutrition. 

The elementary type of a gland or organ of secretion 
consists of a sac, on the interior of the wall of which a 
network of arterial ramifications is spread ; this delivers 
its blood into a similar network of veins. The matter 
the gland is destined to separate oozes from the arterial 
capillaries into the interior of the sac, and is delivered 
through the neck or mouth thereof, which may be spoken 
of as the duct. 

This elementary or typical form of a gland is but very 
little departed from when the sac is elongated into a 
tube ; and even where this has been extended to an ex- 
aggerated degree, the essential principle of action still 
remains the same. 

From the constancy of aspect presented by glands we 
might be led at first to suppose that their peculiarities 
of construction determine their physiological action, that 
the liver secretes bile, and the kidney urine, because 
they have the special organization needful for such pur- 
poses. Such a supposition, however, has to be received 
with much limitation, as is proved by numberless cases 
of vicarious action. Thus, in morbid difficulties of the 
liver, the skin will discharge its duty for it in the elimi- 
nation of the bile. 

The secretion of material from the blood may be con- 
sidered as conducted in two different ways; 1st, by fil- 
tration ; 2d, by cell action. 

Secretion by filtration is, of course, a purely physical 
act. The transudation of water charged w r ith saline 
substances, or with more or less of albumen, seems to 
imply nothing but the escape of pre-existing bodies 
through pervious or porous membranes. Such a result 
is presented in the case of the lachrymal gland, its duty 
being to accomplish a definite mechanical operation for 
the eye in keeping the cornea clear and transparent. 

What is the object of the function of secretion ? Describe .the 
elementary type of a gland. How do the facts of vicarious action 
bear on the theory of secretion ? In how many modes is secretion 
accomplished ? Give an example of secretion by filtration. 



OF SECRETION. 177 

This mechanical function is again observed in the case 
of the serous membranes, and particularly the synovial 
ones, in which the relief of friction of movable parts 
seems to be the object aimed at. 

Afl long as the material secreted clearly pre-exists in 
the blood, it is needless to refer secretion to any other 
principle than the simple one of transudation or filtra- 
tion. It would be unphilosophical to suppose that the 
lachrymal gland exercises any property for the formation 
or production of water when by mere transudation copi- 
ous supplies of that substance can be obtained from the 
blood. 

But secretion is, moreover, perhaps connected with 
cell life. On the upper part of the intestine of the young 
chick, a few cells make their appearance about the fourth 
day of incubation. They are eventually recognized as 
bile-containing cells from the color of their contents. 
As the process goes on, the spot they occupy buds off, 
as it were, so as to produce a blind pouch. This off- 
shoot, with its exterior cells, is eventually, when perfect 
development is reached, the liver. 

Our conclusion respecting the mode of action of se- 
creting cells turns altogether upon the evidence of the 
power they possess of preparing material not pre-exist- 
ing in the blood. Thus, if it should be shown that, un- 
der normal circumstances, the elements of bile are not 
found in the blood, the inference might be drawn that 
the hepatic cells display a combining, or, as it were, a 
preparing power; and so likewise in the case of other 

xeting cells; but the weight to be attached to such 
evidence is greatly affected by the consideration that 
the action of each gland or secreting apparatus masks 
wbal IB really going on in the system. It is possible 
that we may be scarcely able to discover the traces of 
Bnbstanoefl in the blood, and yet a tendency may exist 
for their accumulation to a great extent. Tims there 
can be no doubt that urea would abound through the 
disintegration of the muscular structures, and the use 
of nitrogen ized food, if it were not for the action of the 
kidneys. It ifl the very perfection of that action which 

liminishea the amount in the circulation as to prevent 

ration by cell action. Why is it so fre- 
quently difficult to detect the prodnctt of secretion in the blood? 

II 2 



178 FILTRATION AND CELL ACTION. 

us, except with difficulty, from detecting the presence 
of the ingredient. 

The cases in which the influence of cells is indisputa- 
ble are those offering to us combinations of progressive 
metamorphosis. Of these, the most striking instance is 
the preparation of the spermatic fluid. Perhaps we 
should not be very far from the truth if we considered 
all those secretions in which the materials are in a state 
of retrograde metamorphosis, or in a descending career, 
as arising by mere filtration, and those ascending to a 
higher grade as due to cell agency ; between the two 
there being an intermediate class, the phase of which is 
stationary, and cells may or may not be necessarily in- 
volved, as, for instance, the transmutation of one fat into 
another, or the preparation of sugar from albuminoid 
bodies. 

The apparatus for secretion is generally conveniently 
treated of under two heads: 1st. Membranes, such as 
the serous and mucous ; 2d. Glands, as the liver, kidney. 
This division is, however, not founded either on struc- 
tural or functional differences, and is to be preserved 
merely for the sake of convenience. 

A secreting membrane consists essentially of a tunic 
of connective tissue, affording a nidus for vessels and 
nerves. Upon this, in the opinion of many anatomists, 
a thin basement membrane is laid, its existence being, 
however, denied by others. Upon the surface of the 
basement membrane there is a layer of cells, differing in 
form and arrangement in different regions. In some 
places the cells are flat, in others cylindroid. Their 
duration is temporary, one brood succeeding another 
from germs in the basement membrane. The super- 
ficial, and, therefore, the older cells, desquamate or de- 
liquesce, and are replaced by others from beneath. 

The fluid exuding from serous surfaces is a dilute al- 
buminous solution, more dilute as it is presented in the 
ventricles of the brain, and more concentrated in the 
synovial cavities, its consistency in the latter case being 
such that it may sometimes be drawn out in tenacious 

What are probably the conditions for nitration and cell action re- 
spectively ? How many forms of apparatus for secretion are there ? 
Describe a secreting membrane. What are the properties of the 
fluid secreted by serous surfaces ? 



PROPERTIES OP MV( i 179 

threads. The mechanical qualities of these various ex- 
udations permit a certain freedom of motion in the parts 
to which they are applied. Thus the secretion of the 
peritoneum facilitates the movements of the abdomin- 
al viscera; those of the pericardium and pleura, of the 
heart and lungs; those of the synovial membranes and 
bursa? mucosae, of the joints and tendons. 

Among secreting surfaces the mucous membranes are 
usually enumerated. Strictly speaking, however, they 
are scarcely so much secreting surfaces as the seat of 
numberless secreting organisms. They line the interior 
of the digestive, respiratory, urinary, and generative ap- 
paratuses, and are characterized by extreme vascularity. 
In structure they consist of several different layers or 
regions, the undermost being submucous cellular tissue, 
upon which is spread the proper mucous membrane, con- 
taining connective and elastic tissue, affording a nidus 
for blood-vessels and nerves. Upon this is the basement 
membrane, covered with epithelial cells. In many re- 
gions this compound structure rises into elevations, as 
in the intestinal villi, or sinks into depressions, as in the 
follicles. 

It is not necessary to give a detailed description of 
mucous surfaces farther than to state that from them 
there is furnished a viscid, glairy fluid, of different shades 
of color from white to yellow, denser than water, and 
insoluble therein. Examined by the microscope, it con- 
tains granular corpuscles and epithelial cells. Its reac- 
tion is alkaline, and its proximate constituent is a sub- 
stance to which the name of mucin has been given. De- 
rived from different sources, as the nasal, bronchial, and 
pulmonary surfaces, the intestinal canal, and the urinary 
and gall bladders, it exhibits specific differences. 

Oj secreting Glands, — The typical form of secreting 
cell-gland is a smirk* cell, with its nucleus at the lower 
end, the other end having become open by deliquescence 
or dehifi and thus constituting a sac. From the 

nucleus thus situated at the end of the cavity broods of 
young cells arise. These become more perfect as they 
advance toward the mouth of the sac. The outer wall, 

What are mucoofl membrmm b? What are the properties ofrau- 

.' Describe the typical f<>rm of a secreting cell-gland. 



180 THE LIVER. 

and especially the region of the nucleus, is furnished co- 
piously with blood-vessels. 

Of such structures, variously modified, different glands 
are composed. We shall now proceed to the descrip- 
tion of the more important of these, as the liver, mam- 
mary gland, etc. 

OF THE LIVER. 

The first appearance of a bile-secreting organ is the 
occurrence of yellow cells variously scattered upon the 
lining membrane of the digestive cavity, as in the hy- 
dra. A concentration or localization next ensues, such 
yellow cells being grouped upon the wall of the intes- 
tine at a definite spot. A csecal projection, in the high- 
er tribes, seems next to force out the yellow cells, bear- 
ing them on its exterior, as in the nudibranchiate gas- 
teropods ; and as these caeca are prolonged more and 
more, so, in a more definite manner, does the rudiment- 
ary liver appear. 

The comparative anatomy of the liver is repeated in 
its order of development in the high vertebrated ani- 
mals. In them it is first detected in an evolution of 
cells, upon the intestinal wall, at the point eventually to 
be the place of discharge of the common bile-duct. This 
agglomeration of bile-cells is next seen to project or bud 
off through the intrusion of a caecal pouch. In the am- 
phioxus the condition thus reached remains permanent, 
and is the counterpart of the liver of a fowl about the 
fourth day of incubation. The caecal pouch next sends 
forth ramifications, likewise accommodated with cells, 
and these, branching again, give origin to a complicated 
structure. In this condition, the mouth of the caecum 
is drawn out and narrowed down, and so forms the ru- 
diment of an hepatic duct. 

In man, the liver is the largest gland in the body : it 
is of a reddish-brown color, dense, and from three to five 
pounds in weight ; convex on its upper, and concave on 
its inferior surface. It has five lobes : the right lobe, 
the left lobe, the lobus quadratus, the lobus spigelii, and 
lobus caudatus. It is held in its position by duplicatures 
of peritoneum and by a fibrous cord termed its liga- 

What is the rudimentary form of the liver ? In what manner does 
its development take place? Describe the liver. 




STRUCTURE OF THE LIVER. 181 

merits. Its peritoneal envelope is the cause of its glossy 
appearance; its cellular envelope extends into the inte- 
rior as sheaths for the vessels. 

The intimate structure of the liver in man is, in many 
particulars, still imperfectly known, though the atten- 
tion of the most eminent anatomists has been devoted 
to it. It may, however, be understood that each hepat- 
ic vein, commencing in the substance of the liver, bears 
upon its capillaries small portions called lobules, from 
the oV to the ^ of an inch in diameter, in a manner 
which calls to mind the Fig, cs. 

arrangement of leaves 
on a branch, or a bunch 
of grapes, as represent- 
ed in Fig. 6S, a being 
the vein ; bbb, leaf-like 
lobules upon its branch- 
es. Excluding the lym- 
phatics, it may be said r ^ (Wf{ 
that four different sys- J L 6 

tems of Vessels are en- Hepatic veins in the lobules of the liver. 

gaged in the liver — the portal vein and hepatic artery, 
the bile-ducts and hepatic veins. The first pair are af- 
ferent, the second pair efferent vessels. The portal vein 
brings the blood from which bile is to be secreted ; the 
hepatic artery brings aerated blood for the nourishment 
of the gland ; the bile-ducts carry away the biliary se- 
cretion which has been separated from the portal blood, 
and the residue, taken charge of by the hepatic veins, 
is eventually carried back into the general circulation 
through the vena cava. 

The arrangement of the four systems of vessels is this. 
The vein originates in the centre of each lobule, and ex- 
hibits a ray-like divergence. On the periphery of the 
lobule the other three vessels ramify. Of these the por- 
tal veinlets dip down into the substance of the lobule, as 

30 do the hepatic arteries, but it is not known whether 
the bile-duel- proceed beyond the surface. The manner 
in which they are related to the secreting cells, and re- 
ceive the liquid yielded by them. i< a Bubjecl of contro- 

What is known respecting it> intimate structure? How many 
• tnu of Teasels are found in the brer? Of these, which are afle- 

rent and which efferent? What i^ the function of each ? 



182 COURSE OF THE BILE. 

versy. Nor is it certainly known whether the hepatic 
artery discharges its blood into the portal capillaries, or 
into those of the hepatic vein. 

The portal blood, as it is preparing to enter the liver, 
may be regarded as systemic venous blood, the consti- 
tution of which has been altered through the additions 
made to it by absorption of matters from the stomach 
and intestine. We may overlook for the present those 
contributions it receives from the veins of the spleen 
and other sources. Regarding it, therefore, as systemic 
venous blood, charged with certain of the products of 
digestion, it enters the liver to be acted upon by that 
gland. The first effect upon it is, in a chemical point 
of view, well marked. The stream setting off to the 
general circulation through the hepatic veins may be 
said to carry away the whole of the nitrogenized mate- 
rial ; for the bile, at this point parted out and sent back 
to the intestine through the biliary ducts, does not con- 
tain more than 4 per cent, of nitrogen, and this exclu- 
sive of the water which imparts to it its liquid condi- 
tion. Arrived in the intestine, a repetition of the same 
process of partition takes place, the coloring matter con- 
taining nearly the whole of this residual nitrogen, being 
dismissed with the feces, and the remaining hydrocar- 
bon taken up by the lacteals along with other fats. 

The first duty of the liver is therefore a separation of 
the nitrogenized principles of the portal blood. These 
are forthwith carried into the general circulation through 
the hepatic veins and the vena .cava. The result is, that 
there is returned to the intestine a sulphureted hydro- 
carbon, still containing so much nitrogen as to form a 
very unstable product, prone even to spontaneous de- 
composition. In the intestine its nitrogen is wholly re- 
moved from it, and the combustible hydrocarbon is then 
absorbed. 

The portal blood, regarded under the aspect here pre- 
sented, is obviously composed of two constituents: 1st. 
Systemic venous blood; 2d. Matters obtained from the 
digestive cavity. We next inquire from which of these 
the bile is really derived. 

What is the portal blood ? What is the first effect of the liver 
upon it ? What course is taken by the bile ? Of what parts is por- 
tal blood composed ? 



SOURCE OF THE BILE. 183 

Besides the presumptive evidence arising from the 
consideration that if the bile originated from matters 
just absorbed from the digestive cavity, it would be in- 
conceivable why it should be returned forthwith there- 
to ; its quality of extreme instability marks it out as a 
substance last approaching to final disorganization and 
decomposition. It bears no aspect of a histogenetic or 
formative body, but, on the contrary, it is on the down- 
ward course. We should scarcely expect to recognize 
it as a primary product of the digestive action, but 
should seek its probable origin in some source of decay. 

Whatever weight may attach to such considerations, 
we have, in addition, direct evidence placing the source 
of the bile beyond doubt by referring it to the systemic 
venous blood, and not to the matters just obtained from 
the digestive cavity. 

During foetal life, the digestive organs are in an inact- 
ive state, but the liver, largely developed, discharges its 
secretion into the intestine. This secretion, known as 
the meconium, is a true bile. 

During foetal life the liver is therefore discharging 
the same function that it does after aerial respiration 
has commenced — that is to say, it secretes bile (meconi- 
um) into the intestine ; but at this period, since there is 
no true digestion, the bile can come from one source 
alone, and that source is the systemic venous blood. 
There therefore can remain no doubt that, in after life, 
the same effect takes place, and that the bile is never 
derived from materials just brought from the digestive 
cavities 

I therefore regard the bile as an excretion of materi- 
als decomposing and ready to be removed from the sys- 
tem. I incline to the supposition that much of it is de- 
rived from the cells of the blood, the life of which is 
only temporary, for the casein of the meconium is noth- 
ing but the globulin of the cells, the two substances be- 
chemicaDy allied, and the predominance of iron in 
the ash of meconium seems to establish a connection 
with haBmatin. 

Bile, from whatever animal it may have been derived, 

From whi the bile derived? What is meconium? 

How does the composition of meconium indicate the source of bile? 
From what source i- its iron derived ? 



184 COMPOSITION AND QUANTITY OF BILE. 

contains a resinous soda salt, a coloring material, choles- 
terine, and mucus. The acid of the soda salt is the tau- 
rocholic or glychocolic. The coloring matter in carniv- 
orous and omnivorous animals is brown, the cholepyr- 
rhin of Berzelius ; but in birds, fishes, and amphibia, it is 
green, biliverdin. 

Bile is secreted more slowly during a long period of 
fasting, and more rapidly during normal nutrition. To 
a certain extent, this variable rate depends on the gen- 
eral principle that a gland acts more energetically in 
proportion as the supply of blood sent to it is greater. 
If not wanted for the present purpose, the product is 
stored up, for a time, in the gall-bladder. 

The flow of bile takes place with different degrees of 
rapidity at different diurnal periods : thus it reaches its 
maximum in from thirteen to fifteen hours after the last 
full meal, and then rapidly diminishes. 

Bidder and Schmidt estimate the diurnal secretion in 
an adult at 54 oz., containing 5 per cent, of solid matter, 
an estimate undoubtedly too high, so far as an average 
diet and state of health are involved. 

But the liver has other duties to discharge besides the 
separation of bile. It gives origin to sugar and fat, as is 
proved by the circumstance that the blood of the hepat- 
ic veins is richer in those ingredients than the blood of 
the portal. In this respect its action seems more par- 
ticularly to be that it converts other sugars into the par- 
ticular form known as liver-sugar, which it can also pro- 
duce from the transforming albuminous bodies ; it forms 
fat from sugar, and makes from certain other fats the 
special one known as liver-fat. In this duty of forming 
sugar and fat, it exhibits an inverse power of action ; as 
the production of the one predominates, that of the oth- 
er declines. 

Does the liver really secrete bile ? Is it the business 
of the so-called bile-secreting cells to withdraw the con- 
stituents of that liquid from the blood, and combine 
them together into this viscid yellow liquid ? I think 
not ; for it is a matter of demonstration that not only 

What are the chief ingredients of bile? Under what circum- 
stances does the secretion of bile vary ? When is its maximum 
flow? What is its diurnal amount? What other substances be- 
sides bile does the liver secrete ? 



ACTIOX OF THE LITER OX BLOOD-CELLS. 185 

every constituent of the bile, but the bile itself, pre-exists 
in the blood, and it is just as unphilosophical to burden 
those cells with the duty of forming it as it would be to 
believe that a like agency is needful for the appearance 
of urea in the kidney. 

For such reasons, I believe that the bile simply trans- 
udes from the blood, and that the cells of the lobules 
have no special relation to it beyond this, that it oozes 
past their interstices, or, perhaps, by physical imbibition, 
finds access to their interior. I see no reason that these 
cells should form it when it pre-exists in the blood, nor 
does the state of the affluent and effluent blood offer any 
contradiction to this conclusion. In all discussions of 
the functions of this organ founded upon a comparison 
of the portal and hepatic venous blood, the relative quan- 
tity of water they contain, and its great and even rapid 
fluctuations, should always be borne in mind. As might 
be expected, portal blood contains far more water, and, 
even after abundant drinking, the amount in the hepat- 
ic venous blood has by no means increased to the extent 
that might have been expected. It is for these reasons 
that the tale varies so greatly at different periods in its 
specific gravity and fluidity. 

The liver, besides producing sugar and fat, is the seat 
of disintegration of the worn-out blood-cells, and here 
probably the young ones are pushed forward through a 
certain stage of their development ; advantage, more- 
over, being incidentally taken of the secreted bile, which 
< properties useful though not essential for pro- 
moting the digestion and absorption of fatty material, 
perhaps, also, of imparting a definite course to the trans- 
mutation of the semi-digested material in the intestine, 
and this both as regards nitrogenized, amylaceous, and 
fatty bodies. Of the influence of the bile in promoting 
the absorption of fat, the physical experiments hereto- 
fore alluded to leave no doubt ; but that these uses are 
of a secondary or non-essential kind, and are only taken 
advantage of in an indirectly economical way, is estab- 
lished beyond all possibility of a doubt by the fact that 
animals can live for a long time, even for months, with- 
out the of bile into the intestine, provision hav- 

What action has tne liver on old hlood c 



186 THE FOUR-FOLD ACTION OF THE LIVER. 

ing been made for its escape externally through an ar- 
tificial fistulous orifice. 

These conclusions respecting the functions of the liver 
are in harmony with the appearances presented by the 
blood leaving and entering it : the predominance of col- 
orless blood-cells, and of young cells well advanced to- 
ward perfection in the former, and of wasted, worn-out 
ones in the latter ; with the fact that the maximum se- 
cretion of bile does not take place until more than half 
a day after the ingestion of food ; and that during foetal 
life, in which there is no food, either in the stomach or 
intestine, to be digested, the liver is nevertheless in high 
activity, and bile is secreted. 

In view of all the preceding facts, we may therefore 
finally conclude that there are at least four distinct op- 
erations conducted in the liver: 1. The production of 
sugar and fat; 2. The separation of the bile; 3. The 
destruction of old blood-cells ; 4. The completion or per- 
fection of young blood-cells, perhaps by receiving their 
iron. With respect to these it may be remarked, 

First. The formation of sugar and fat, either from 
carbohydrates, or what, in this instance, is more prob- 
able, from albuminoid bodies brought by the portal vein, 
can no longer be doubted. The prevalence of liver- 
sugar and liver-fat in all that region of the venous cir- 
culation included between the liver and the lungs must 
be attributed to this source. That the sugar undergoes 
rapid metamorphosis in the pulmonary organs is plainly 
proved by the effects of irritation of the pneumogastrics, 
which, interfering with the function of respiration, per- 
mit this substance to reach the aortic circulation, from 
which it is removed by the kidneys, diabetes arising. 
So far as the preparation and course of this sugar is con- 
cerned, the liver is a ductless gland. The production of 
fat appears to be inversely as that of sugar. 

Second. The bile is separated from the blood portion 
of the portal blood, and not from the products of di- 
gestion obtained from the chylopoietic viscera. The 
elements of bile pre-exist in the blood, and escape from 

What action has the liver upon young blood-cells ? Mention the 
four operations conducted in the liver. In "what manner does the 
sugar produced disappear ? How does the bile escape from the por- 
tal veinlets into the biliary ducts ? 



SUMMARY OF THE ACTION OF THE LIVER. 187 

the portal veinlcts to the biliary ducts by mere filtration 
or strainage. The precise source from which the bile is 
derived is probably the blood-cells, and in the changes 
they are undergoing the spleen is perhaps concerned. 
If this be so, the bile-duct is as much a duct for the 
spleen as it is for the liver itself. The bile may almost 
be looked upon as a hydrocarbon, containing a very 
changeable and therefore noxious coloring material ; 
this, when the secretion reaches the intestine, is parted 
from it and dismissed with the feces, the proper hydro- 
carbon being taken up by the absorbing arrangement 
for hydrocarbons, the lacteals, and so sent through the 
thoracic duct. Perhaps, also, by reason of its special 
adaptedness for that purpose, it aids in the absorption 
of other tats. 

At this point it may be remarked that the view here 
presented of the sugar-forming and bile-straining func- 
tions of the liver appears to be greatly strengthened by 
the anatomical construction of that organ. There is no 
obvious communication between the portal and hepatic 
veinlets save through cells, but the portal veins and the 
bile-ducts run in their ramifications side by side. 

Third. Whatever part of the disintegration of old 
blood-cells takes place in the spleen, their final destruc- 
tion is doubtless accomplished in the liver, this being 
the immediate source of the bile itself. Though these 
metamorphoses are, to a greater or less extent, occur- 
ring throughout the circulation, it is in these two great 
that an opportunity is afforded for the destruc- 
tion to reach its completion, and the resulting product 
of waste to be removed; nor is there any thing in this 
view at all contradictory to the opinion that all the con- 
stituents of the bile may be found in the general circu- 
lation. 

Fourth. The liver also aids in the preparation or ma- 
turation of young blood-cellfl in an indirect way. There 
are certain of the mineral constituents of the disinte- 
grated cells too valuable i<t away, since they can 
subserve the duty of entering into the composition of 
yon ling toward perfection. As such a sub- 
ace maybe mentioned iron. This view of the action 

In what ]■■ iivr-r and spleen relet i? How docs the 

liver promote the maturation of young Mood-* 



188 THE DUCTLESS GLANDS. 

of the liver appears also to be sustained by the large 
number of star-like and corrugated blood-cells occurring 
in the portal blood of fasting animals, and which are re- 
placed by such as appear to be young and perfect in the 
blood of the hepatic veins. It is not, however, to be 
supposed that all the iron is economized in this manner ; 
a considerable portion of it accompanies the pigment as 
an essential ingredient, and is finally discharged through 
the intestine. 

OF THE DUCTLESS GLANDS. 

The salivary and sudoriparous glands discharge their 
secretion directly through ducts. The liver and kid- 
neys have upon their ducts an additional mechanism, 
the gall bladder in the one case, and the urinary in the 
other. These serve as receptacles for storing up the 
product of action in a temporary manner, and so con- 
verting the continuous effect of the gland into a period- 
ical result. In each of these instances we may arrive at 
conclusions of a certain degree of exactness respecting 
the functions and use of the gland from a study of the 
secretion it yields ; but there are in the system other 
glandular organs differing essentially from all the pre- 
ceding in not being furnished with ducts. These are 
the spleen, the thymus and thyroid glands, and the su- 
pra-renal capsules. 

Much diversity of opinion prevails respecting the true 
nature and action of these bodies. From their struc- 
ture bearing a resemblance to that of the preceding, 
with the exception of the absence of a duct, many have 
thought that, like them, they are really secreting organs. 
Others have supposed that they have a relation to the 
nutrition of the system, in giving origin to the develop- 
ment of cells, or that they are connected with the organ- 
ization of the blood itself; and that such is their duty 
is perhaps rendered probable by the circumstance that 
some of them, as the thymus and thyroid, exhibit their 
utmost development when the body is rapidly growing, 
and diminish when maturity is reached. That they en- 
joy a community of action, or that their function can 
be vicariously discharged by other organs, has been 

Is all the iron economized in this manner? Give examples of 
ductless glands. What are their supposed functions ? 



THE SPLEEN. 189 

clearly established by the result of operations in which 
one or other of them has been extirpated. 

With respect to the spleen, the views of Professor 
Kolliker are supported by many facts. He supposes 
that one of the chief functions of that gland is the disso- 
lution of the disorganizing blood-cells preparatory to the 
action of the liver, in which haunatin is to be converted 
into the coloring matter of the bile. In the discussion 
entered into respecting the origin of the bile, we have 
come to the conclusion that it is derived from the sys- 
temic venous blood, and in the supposition here present- 
ed respecting the functions of the spleen there is noth- 
ing contradictory, for it is to be remembered that the 
blood of the spleen is a constituent of the portal circu- 
lation. It also appears to be a general opinion that the 
spleen likewise maintains a mechanical relation to the 
portal mechanism by serving as a receptacle for any ex- 
cess of blood, and thus relieving the vessels of pressure, 
or by acting in like manner when there is any obstruc- 
tion to the passage of blood through the liver. 

As our knowledge of the action of the ordinary glands 
becomes more accurate, the function of the ductless 
glands loses much of its peculiarity. As we have al- 
ready stated, in a certain sense the liver itself may be 
said to be a ductless gland, for it appears to be one of 
the constant duties of that organ to prepare sugar from 
materials in which it did not pre-exist. And this sugar 
does not escape through the hepatic ducts in company 
with the bile, but is taken directly into the system 
through the hepatic veins. But this principle of action 
ifl identically what occurs in the case of every ductless 
gland, and hence it may be inferred that the changes 

impr. 1 by them on the blood are necessary for the 

development and nutrition of the system. If the doc- 
trine of Kolliker be correct, the spleen is onlvan appen- 
dix to the liver, and the same duct answers as a common 
outlet for both. 

Dr. Henry Draper investigated the functions of the 

sen in 1856 by the aid otmioroecopic photography. 

Tie followed w.'i< to take a drop of blood 

What i"n of the spleen on blood-cells? What, 

mechanical duty da ? What is in reality the dud 

of the spleen ? 



190 OF EXCRETION. 

from the splenic vein of an animal, and, at the same 
time, on an another slip of glass, a drop from an artery 
in the leg. These were photographed, and the photo- 
graphs then submitted to a careful inspection and count- 
ing. The blood from the leg gave a standard of com- 
parison, and the effect of the spleen was of course fully 
seen in that issuing from the splenic vein. The conclu- 
sion he arrived at was, that " splenic venous blood con- 
tains at least double the general average of imperfect 
blood-discs, and therefore the spleen is an o/gan for the 
disintegration of the blood-discs." 



CHAPTER XII. 

OF EXCRETION. 
THE URINE, MILK, AND CUTANEOUS EXCRETIONS. 

Of the Kidney : its Structure and Functions. — The 
Malpighian Circulation. — The Urine. — The Water 
and Salts exude by Filtration, — The Cells remove 
unoxidized Bodies. — Marnier of Removal of the Liq- 
uid from the Malpighian Sac. 

Of the Mammary Gland: its Structure. — Colostrum 
and Milk. — Ingredients of Milk. — Influence of Diet. 
— Inquiry into the Origin of the Ingredients of the 
Milk, its Fat, Casein, Salts, Sugar. — Manner of Ac- 
tion of the Gland by Strainage. 

Of the Skin.- — Structure of its Epiderma and Derma. 
— Sudoriparous and Sebaceous Gla?ids. — Ingredients 
of Perspiration. — Exhalation : its Amount. — Causes 
of the Variable Action of the Skin. — Its Double Ac- 
tion. — Absorption by the Skin. — General Summary 
of the Cutaneous Functions. 

OF THE KIDNEY. 

The non-gaseous products of waste arising from oxi- 
dation in the functional activity of the system, the use- 
less materials, saline or otherwise, absorbed in the di- 
gestive tract, and carried into the circ ulation, must be 

What is the ratio of imperfect blood-discs found in photographs of 
the blood of the spleen ? 



STRUCTURE OF THE KIDNEY. 



191 



removed. Gaseous substances and vapors may pass 
away through the lungs, but solid material must be ex- 
creted in a state of solution in water. To accomplish 
this object, a special mechanism, the kidney, is intro- 
duced. 

In man the kidneys may be described as a pair of 
dark red ovoid bodies, placed one on each side of the 
vertebral column, in the lumbar region, the right kidney 
being a little lower than the left. In the adult the kid- 
ney is four or five inches in length, and is enveloped in 
a mass of fat. Blood is brought from the aorta to sup- 
ply the organ by the renal or emulgent artery, and is 
carried back by the emulgent vein into the inferior vena 
cava. During its passage through the kidney there is 
removed from the blood a liquid secretion, the urine, 
which, flowing down a long channel, the ureter, is emp- 
tied into the bladder, from which it may be periodically 
removed. 

The supra-renal capsules are bodies of a yellow-red 
color placed above the kidneys. They are much larger 
in the foetus than in the adult, and doubtless have a ref- 
erence to the peculiar conditions of respiration obtain- 
ing at that time. 

The substance of the kidney is 
described as consisting of two 
portions, the cortical and the 
medullary or tubular, as seen in 
. 00, in which 1 is the supra- 
renal capsule ; 2, the vascular 
portion of the kidney; 3 3, tubu- 
lar portion grouped into cones ; 
4 4. papillae projecting into cali- 
5 5, the three Lnfnndibu- 
la: I Ivia ; 7, the ureter. — 

(Wilson.) From this it. appears 
that the cortical Bubstance i> the 
external portion, and the tubular 
grouped into cones, tin- base 
of each cone being outward, and 
the point toward the pelvis of 



Fig. 69. 




Inej. 



What class of substances u removed by the kidney ? What i- the 
•ion and anatomy of the kidney? Where arc the inpra-renal 
- With what function do they leem to he connect 



192 THE MALPIGHIAN CORPUSCLES. 

the kidney. The cortical substance, however, envelops 
the cones nearly to their points. It is of a red color, 
and is the seat of the secreting action. The urine, as it 
arises, passes along the fine convergent vessels, the uri- 
niferous tubes, and these, coalescing as they approach 
the points of the cones, give origin to what are termed 
the ducts of Bellini. From these the secretion passes 
into the calices, thence into the pelvis, and so along the 
ureter into the bladder. In the cortical substance there 
are large numbers of dark points, the Malpighian bodies. 
Their diameter is about y^ of an inch. 

Mr. Bowman has demonstrated that the minute struc- 
ture of the cortical portion is as follows : The urinifer- 
ous tubes, as they approach it, undergo bifurcation in 
such a way that the branches continually arising have, 
for the most part, a diameter of about -^j of an inch. 
As they enter it they are contorted, and at their ends 
present small capsules or flask-shaped sacs. Each of the 
capsules is entered by a twig of the renal artery, which 
at once divides into loop-like branches constituting a 
tuft, and delivering the blood to a vein originating in 
the interior of each tuft. These structures are known 
as the Malpighian corpuscles. The vein and artery pass 
out of the corpuscles usually at the same point ; the 
vein, however, instead of delivering its blood at once to 
the renal vein, forms a plexus on the sides of a urinifer- 
ous tube. It is supposed that the exudation of the wa- 
ter of the urine takes place in the Malpighian body, and 
the secretion of the solid portions from the cells cover- 
ing the uriniferous tubes. 

The chief feature of this structure is, therefore, that 
in a sac formed upon a uriniferous tube, a tuft of capil- 
laries, the walls of which are of extreme tenuity, permits 
water to escape from the blood supplied by the emul- 
gent artery. The blood, thus concentrated by loss of 
its water, passes into the veinlets originating in the in- 
terior of the tuft ; these, converging into a little trunk, 
less in diameter than the twig of the emulgent artery, 
escape along with that vessel from the capsule ; but, in- 
stead of discharging its contents into the renal vein, it 

Describe the course followed by the urinary secretion. What is 
the constitution of the Malpighian bodies ? Describe the course of 
the circulation in the kidney, 




MALPIGHIAN CIRCULATION — THE UIIIXE. 193 

ramifies in a plexus on the walls of a uriniferous tube, 
thus affording a miniature representation of the portal 

vein, beginning in a capillary sys- 7.7,,. to. 

tern and ending in one. From //^=^ 

the plexus the commencing capil- /Y 

laries of the renal veins arise. C^ir-^^ 

Mr. Bowman's explanation of " n_r — 

the Malpighian circulation is rep- =^ x 
resented in F<y. 70. a, branch ; 

of renal artery; af, afferent ves- fjftg%, t* ^^^^ 
//?, Malpighian tufts ; ef JSgL/ ^ 
Liferent vessels ; ^>, their plex- ^MF 
tin upon the uriniferous tube ; st, ™> 
straight tube; <?t, convoluted tube. 

The urine of man is a clear, am- 
ber-yellow liquid, the average spe- 
cific gravity of which may be tak- 
en at 1.020, giving an acid reaC- Diagram of Malpighian cin 

tion when first voided, but gradu- lation - 

ally becoming alkaline and turbid. Its composition va- 

- greatly with preceding states of the system, and the 
nature and quantity of the food. It amounts, in the 
course of a day, to from 20 to 50 ounces ; this, however, 
depending on the quantity of water that lias been taken, 
and on the activity of the skin. Its solid ingredients 
vary from 20 to 70 parts in 1000 of the urine, the lead- 
ing substances being urea, uric acid, lactic acid, vesical 
mucus, epithelial debris, extractive, and salts. 

Viewed as a group, the constituents of the urine arc 
evidently the oxidized residues of the system, which, un- 
able, from their not possessing the vaporous or gaseous 
fori ape through the lungs, are, from their solu- 

bility in writer, readily removed by the kidneys. The 
area and uric acid arc derived from muscular decay; 
ihe two, the uric acid first arises, and is sub- 
erted into urea; this is not, however, its 
since the quantity of urea increases by 
the use of highly nitrogenized food. The mucus and 

In what n ble the porta] circulation? Explain 

tic- Malpighian circulation. Wig* 7<>. What arc. the 

properties and quantity of the urine? To what - 
do its constituents belong ? From what Kmrcet arc the area and uric 

T 



194 COMPOSITION OF THE URINE — UREA. 

epithelial debris are derived from the mucous mem- 
brane lining the interior of the urinary apparatus. Of 
the salts, there are two of unusual interest, the sulphates 
and phosphates, each having, like the urea, a double ori- 
gin, the food and tissue decay. Leaving out of consid- 
eration that part which has been supplied by the food, 
we recognize in the sulphates the final disposal of that 
sulphur which was once secreted by the liver, and sub- 
sequently reabsorbed. In the phosphates we recognize 
the oxidation of the phosphorus of the nervous vesicles 
during their period of activity. That portion of the sol- 
id constituents of the urine due to decay or retrograde 
metamorphosis is shown when an animal is exclusively 
fed on sugar. 

The composition of urine is not only disturbed by 
variations in the amount of its normal ingredients, but 
likewise, in morbid states, by the appearance of unusual 
ones. Among these may be more particularly mention- 
ed sugar, albumen, blood, bile, pus, fat. The presence 
of such abnormal ingredients is determined by chemical 
tests or microscopic observations. 

In his inaugural dissertation, entitled, " Is Muscular 
Motion the Cause of the Production of Urea ?" Dr. John 
C. Draper, by experiments on the urine of persons in 
different conditions of motion and rest, and by an ex- 
amination of the diurnal and nocturnal variations in the 
amount of urea voided, compared with an invariable 
standard, gives reasons for concluding that the differ- 
ences in the amount of urea excreted are almost entire- 
ly attributable to the influence of the food, an individ- 
ual in such a state of comparative rest as is observed 
during treatment for a fractured leg not excreting by 
any means so much less urea as might have been an- 
ticipated when compared with another individual who 
walked thirteen miles at the rate of four and a half 
miles an hour. 

But, on examining the influence of food, it appears to 
be well marked. The greatest amount of urea is ex- 
creted within a few hours after dinner. Another maxi- 

From what source is the mucus derived ? From what the sulphates 
and phosphates? What unusual substances may occur in urine? 
What reasons are there for supposing that urea is mainly due to the 
ingestion of food ? 



KEMOVAL OF URINE SALTS. 195 

mum also occurs just after breakfast; but during the 
x night hours fiur less is excreted than during the 
same period in the afternoon. 

The ingestion of food thus exercising so rapid and 
marked an influence on the quantity of urea, he refers 
to it as the cause of the increased excretion of that sub- 
ce during the course of the day rather than to the 
increased motion of exercise then indulged in ; and in 
view of this conclusion, it becomes probable that the ni- 
trogen of the wasting muscular tissues escapes, not un- 
der the form of urea through the kidneys, but through 
the skin, or perhaps even as free nitrogen from the 
lun_ 

Ot medicaments and other unusual substances intro- 
duced into the organism, those that are soluble in water, 
and have little affinity for the constituent matters of the 
body, are removed in the urine. In this list are found 
a great number of salts escaping in this manner without 
undergoing any change ; such, for example, as carbonate 
of potash, nitrate of potash, bromide of sodium. Other 
substances undergo change previously to their elimina- 
tion, as, for instance, the alkaline sulphides, which be- 
come oxidized, and are then finally removed as alkaline 
sulphates. 

The anatomical construction of the Malpighian bodies 
lias led physiologists to infer that there are two distinct 
stages in the secretion of urine. These have already 
been pointed out in the remark that the Malpighian 
bodies separate water from the blood, but that the solid 
.edients are secreted from the delicate plexus of ves- 

- covering the walls of the urinary tubes. Before ac- 
cepting this opinion, we may, however, observe, that the 
chief solid constituents of the urine, as* urea, uric acid, 
sulphates, and phosphates, pre-exist in the blood, and 
are all soluble in water. It is not to be supposed that 
the water rough the delicate walls of the Mal- 

. nan tu: 1 leave such substances behind it. 

it the loss of water actually takes place in the tuft 

fact that the 
tn the ti - than the one enter- 

mored from the*feyBtem bj the kid- 

known t!. 



196 REMOVAL OF UNOXIDIZED SUBSTANCES. 

ing it; the volume of blood is less by the amount of ab- 
stracted water. 

We must, moreover, take care that we are not de- 
ceived by a name. The vessel emerging from the tufts 
may be conveniently enough called a vein^ but is there 
any proof that such is its physiological attitude ? There 
is no reason to brieve that the blood has lost its arterial 
character while it has been in the tuft. At the most, it 
can only have lost the elements of urine. It is not until 
it is distributed in the plexus on the walls of the urinifer- 
ous tubes that it really gains the venous character, and 
then through nourishing those vessels, and particularly 
the cells of their interior. 

These considerations therefore lead me to the sugges- 
tion that the inorganic bodies, as urea, uric acid, sul- 
phates, and phosphates, pass out with the water in which 
they are dissolved while the blood is yet circulating in 
the Malpighian tuft. The loss of velocity in the current 
by the arterial twig breaking up into so many vessels 
must, as Mr. Bowman states, greatly favor this transuda- 
tion, as does also the pressure that must arise from the 
blood having to pass through a narrow channel of exit, 
and still more through another capillary system just be- 
yond. It was arterial blood that entered the tuft, and 
it is arterial blood that emerges, to be then directed 
upon the walls of the uriniferous tubes. 

And now the question may arise, What is the object 
of this second capillary circulation? Though the state- 
ment is often made that the constituents of the urine 
are the results of oxidation, it is very far from being 
strictly true. The analysis of urine shows that a very 
large proportion of them, classed as extractive, are real- 
ly combustible bodies, and not far advanced in their ret- 
rograde metamorphosis. They retain still, as it were, 
the traces of organization ; they belong rather to the 
hydrocarbon family than to the nitrogenized. It may 
be that, for the removal of these, cell action is necessary. 

Whatever importance may be attached to such a sug- 
gestion, it is very clear that, notwithstanding the ex- 
treme thinness of the walls of the tuft vessels, the relax- 
ation in the sp^ed of the blood current through them, 

Why must saline substances accompany it ? What is the object 
of this second capillary circulation ? 



THE MAMMARY GLAND AND ITS STRUCTURE. 197 

and the pressure brought to bear upon them, that water 
could not be separated by oozing through them unless 
there was an additional provision. The sac into which 
the exudation is to take place is already full, and it may 
be questioned whether ciliary motion in the uriniferous 
tubes would exert a sufficient exhaustion to relieve the 
interior of the capsule from pressure; but the introduc- 
tion of a liquid of a different nature into the uriniferous 
tube may call at once into operation the principle acting 
in the capillary circulation of the blood, and thus the 
contents of the Malpighian sac are drawn forward into 
the uriniferous tube, just in the same manner that water 
is drawn from the inside of a bladder through the pores 
thereof by alcohol on the outside. 

THE MAMMARY GLANDS. 

The mammary glands are situated on various portions 
of the abdominal and thoracic surfaces of animals of the 
class mammalia. In the higher members of this class 
they present the appearance of racemose glands, rudi- 
mentary in the males, but well developed in the adult 
females, especially after parturition. They separate from 
the blood the white secretion, milk. 

In different cases the number of mammae differs. In 
the human species there are but two, placed upon the 
thoracic surface, and from their position favoring the 
care and nursing of the child. Among other animals 
the number seems to have a relation to the number of 
young brought forth at a birth, there usually being a 
pair for each one. Many exceptions to this rule, how- 
ever, occur. 

The mammary gland corresponds in anatomical struc- 
ture to the parotid and pancreas. It consists of 15 or 
LCD from \ to 1 inch in width ; these are com- 
f lobules, and these, again, ofca-cal vesicles. The 
ry ducts are lined with tcsselated epithelium. 
Til- converge toward the nipple, opening upon it 

by 10 or 16 apertures, and in their 0OUTS6 dilating into 
ampulla-, of small capacity in women, but in the cow ca- 
pable of holding a quart. 

What u the m I <>f the liquid from the Malpighian 

nunary gland ? What number is there usu- 
ally of them? What u its anatom 



198 



COLOSTRUM AND MILK. 




Section of the human 
mammary gland. 



Fig. 72. 



Fig.n. j?ig m yi ? vertical section of the hu- 

man mammary gland : a a, its pectoral 
surface ; b 5, skin on surface of the 
gland ; c, skin of nipple ; rf, lobules and 
lobes of gland; e, lactiferous tubes pass- 
ing from the lobules to. the nipple. 

Milk globules are minute particles, 
varying in their diameter from the 
winr to the l 3 * o of an in c°- They 
consist of oily material inclosed in an 
envelope, as is shown by the fact that, 
though they will resist for a short time 
the action of sulphuric ether, they are 
finally dissolved by that substance. Be- 
sides these milk globules, there are other exceedingly 
minute fat particles present. The 
milk which is first secreted con- 
tains corpuscles of considerable 
size, and of a granulated appear- 
ance, as seen in the photograph, 
Fig. 72. They are called colos- 
trum corpuscles. They are solu- 
ble in ether, and therefore con- 
tain fat. There is reason to sup- 
pose that all the fat globules of 
the milk are inclosed in cyst-like 
pellicles of casein. 
In the chapter on food (Chapter II.), a general de- 
scription of the character and constitution of milk has 
been given, together with its physiological relations in 
nutrition. It may now be added that fresh milk pre- 
sents an alkaline reaction. Left to itself, and the more 
quickly the warmer the air, milk turns sour through the 
production of lactic acid, the casein undergoing coagu- 
lation. That the oil globules just spoken of are coated 
with a film of a coagulated protein body appears from 
the circumstance that it may be dissolved by acetic acid, 
and the included butter is then set free. 

The composition of milk varies with many circum- 
stances. Thus, among cows, it is well known that there 
are certain breeds yielding a milk in which butter pre- 

Describe the section, Fig. 71. What are milk globules? What is 
colostrum ? What are the properties of milk ? 




Milk with colostral corpuscles. 



ACTION OF THE MAMMARY GLAND. 199 

dominates ; in others, a milk containing an excess of 
casein. It is in reference to this that such are, among 
agricultural people, often described as good butter cows, 
or good cheese cows, as the case may be. Such varia- 
tions are likewise often popularly referred to peculiari- 
ties in the color of these animals ; and, indeed, there is 
a general impression of the same kind as respects the 
milk of women, that that of fair women is inferior to 
that of brunettes. 

As would be expected, the constitution of the milk 
varies greatly with the diet. Simon found that in the 
case of a very poor woman, who had been almost de- 
prived of the necessaries of life, the quantity of solid ma- 
terial was only 8.6 per cent. On giving her a nutritious 
meat diet it rose to 11.9 per cent. Being again reduced, 
by circumstances, to the utmost destitution, the solid 
residue sank to 9.8 per cent.; and on once more being 
supplied with nutritious meat diet, the percentage rose 
to 12.6. 

The diurnal quantity of milk yielded by the human fe- 
male has been estimated at from 32 to 64 ounces. This 
estimate is made by determining the weight of the in- 
iant before and after suckling. Although a certain pro- 
portion is present in the gland, the secretion appears to 
take place for the most part with great rapidity. On 
the application of the infant the blood flows suddenly, 
and the milk pours into the ducts, constituting w T hat is 
termed the draft. 

We now enter on a consideration of the function of 
the mammary gland, with a view of determining wheth- 
er it acts in virtue of its special construction, whether it 
lubricates in itself, by the agency of cells, the proximate 
constituents of milk, or whether it merely strains them 
from the blood in which they pre-exist. 

Due weight should here be given to the fact that, un- 
like the excretions of the lungs, the kidneys, or even 
liver, the milk contains a large percentage of histo- 
letio or formative bodies. Its casein cm not be con- 
iu the career of retrograde transformation, 

In what I- composition vary ? What effect have va- 

riations of diet OH inilk ? What is its diurnal quantity? How is it 

known that the structure of the mammary gland is not essential to 
the secretion of milk ? 



200 SPECIAL STRUCTURE — SALTS. 

since in the body of the infant it is presently changed 
into albumen. Such a fact might even lead us to sus- 
pect that we should detect some essential structural and 
functional differences between the mammae and other 
glands. 

The influence of special structure is, however, dis- 
posed of by the numerous well-authenticated cases now 
on record, in which portions of the skin, or the stomach, 
the navel, intestines, the axilla, and glands in the groin 
have assumed a vicarious action, and secreted milk;* 
and though it has been said of the latter instance that 
it may be nothing more than an obscure manifestation 
of an attempt in the human species at a repetition of 
the mammary gland in a region near which it is nor- 
mally present in the lower mammals, such a remark has 
no application in the other cases. We may therefore 
infer that the proximate constituents of the milk are 
not manufactured by reason of any special structure of 
the gland secreting them, since other structures can as- 
sume a vicarious action. 

This therefore narrows our inquiry down to the point, 
Does the mammary gland merely filter off from the 
blood substances already existing in it, or, those sub- 
stances not so pre-existing, are they made in this organ 
by cells ? 

Of the proximate elements of milk, many, such as the 
entire group of its salts, are acknowledged on all hands 
to pre-exist in the blood ; and these, constituting about 
■^ of its solid ingredients, must be admitted to pass 
into the secretion by strainage only. Of the other sol- 
id ingredients, the fat, constituting about one fourth, 
also exists in the blood, being derived by lacteal absorp- 
tion from the food. 

Do milk-giving animals, then, find in their ordinary 
diet a sufficient quantity of oleaginous material to sup- 
ply the drain established through the mammary gland, 
and the calorifacient demand, supposing none to be 
made in the system? The researches of Dumas have 
definitely settled this question. Of these the following 
is an abridgment : 

What instances of vicarious action have been recorded ? Do the 
salts of milk pre-exist in blood? Do the hydrocarbons exist in 
food? 



SOURCE OF THE BUTTER OF MILK. 201 

Fat in Articles of Forage. 

Indian Corn 8.75 per cent. 

Rice 1.00 " " 

Oats 3.30 " " 

Rye 1.75 " " 

Wheat 2.10 " " 

Dry Hay 2.00 " " 

Clover in flower 4.00 " " 

Wheat Straw 3.20 " " 

Oat Straw 5.10 " " 

Beet-root 0.05 " " 

Potatoes 0.08 " " 

A cow in good condition, eating 100 pounds of dry 
hay, will furnish 21 quarts of milk, from which there 
can be obtained l£ pound of butter. If this butter was 
obtained exclusively from the food, and none made in 
the system, we ought to find in the 100 pounds of dry 
hay lj pound of fatty matter; but sulphuric ether can 
remove from such hay 2 pounds, and in several speci- 
mens of clover cut in flower, M. Boussingault found the 
proportion as high as 4 per cent. We may therefore af- 
firm, relying on the universal experience of farmers, that 
the hay eaten by a milch cow contains more fat matter 
than the milk she yields. 

There are many facts showing that the identical fat 
occurring in the food is actually delivered by the mam- 
mary gland with many of its qualities unchanged. 
Thus, if by chance cows eat the tender shoots of pine- 
trees, or wild onions, or other strong-smelling herbs, 
the milk is at once contaminated with the special flavor 
of their oils. The same, too, takes place when turnips 
are introduced in their diet. If half the allowance of 
hay for a cow is replaced by an equivalent quantity of 
linseed-cake, rich in oil, the cow maintains herself in 
1 condition, but the milk produces a butter more 
than usually soft, and tainted with a peculiar flavor de- 
rived from the linseed oil. 

To the | '(ding facts it is unnecessary to add any 
observations in relation to the carnivorous animals, 
which obviously find in their prey large quantities of 

ion the i of fill in somr- of the leading articles of 

forage. What general conclusion i< come t<> in the case of the milch 
is it known that the identical fat of the food occurf in 
the milk? 

I 2 



202 CASEIN — ITS SOURCE. 

fat. In the chapter on calorifacient digestion, and in 
that on the functions of the liver, the evidence was pre- 
sented both as regards the reception of oily material 
from the food, and likewise its fabrication in the system. 
From these sources conjointly it may therefore be plain- 
ly seen that fats of various kinds must always exist in 
the blood. A simple arithmetical computation, found- 
ed on the data furnished by the tables of the constitu- 
tion of blood and of milk respectively, will show that 
there is at any moment a sufficient supply of fatty mat- 
ters in the blood to furnish two thirds of the diurnal 
amount of milk. It does not seem, therefore, philosoph- 
ical, under the circumstances, to impute to the mamma- 
ry gland a power of forming butter. 

Next of the casein. There has been much controver- 
sy among chemists respecting the existence of casein as 
a normal ingredient in the blood. Theoretically there 
does not appear any solid reason for denying that it 
may be one of those constituents, considering its analo- 
gy of constitution to albumen. The evidence is much 
more distinct and positive in the case of puerperal blood, 
and is greatly strengthened by the recognized tendency 
to the occurrence of kiestine in the urine during gesta- 
tion. 

The occurrence of casein under the form of kiestine 
in the urine, in quantity increasing as gestation ad- 
vances, indicates therefore that the system is assuming 
a propensity for the generation of this substance from 
its albuminoid compounds ; and since, in cases of starva- 
tion, the percentage of casein in the milk does not seem 
to be materially affected, we are to attribute its imme- 
diate source to the system rather than to the food. In 
this respect it differs from the oily constituent, butter, 
the percentage amount of which is instantly affected by 
variations in the nature and quantity of the food. It 
would seem, indeed, that, from the same plastic ingre- 
dient, albumen, the soft tissues of both mother and in- 
fant are fabricated, with this difference, that in the lat- 
ter case the temporary condition of casein is intermedi- 
ately assumed. There is reason to conclude that casein 

What quantity of fatty matters exist in the blood ? What rea- 
sons' are there for supposing that casein exists in the blood ? Under 
what circumstances does kiestine occur ? 



ORIGIN OF SUGAR IX MILK. 203 

is directly derived from the system, which can manufac- 
ture it at a rate of about 30 grains per hour, this be- 
ing about one half the quantity of fibrin generated in 
the same period of time for the support of the muscular 
tissues. Chemically, the transition from albumen to 
in is not to be regarded either as an ascending or 
declining metamorphosis, but only as the temporary as- 
sumption of a state of passage on ward to the condition 
of fibrin. 

The remarks just made respecting the origin of casein 
are applicable to the saccharine constituent of the milk, 
the origin of which is not to be attributed so much to 
the food directly as to the system ; for, in starvation, 

jar, like casein, still continues to form to nearly the 
normal amount. I think it is probable that its produc- 
tion is due to the liver, and is, in reality, nothing more 
than an indication of the continued action of that gland, 
one of the prime functions of which is the generation of 
saccharine compounds. 

From the data now before us respecting the origin of 
the different constituents of the milk, casein, butter, sug- 
ar, and salts, we are able to come to a definite conclu- 
sion regarding the physiological action of the mammary 
gland. I have entered on this disquisition from the im- 
portant bearing the decision we arrive at has upon the 
whole theory of secretion ; for if there be a gland in the 
body in which we should expect to find proofs of forma- 
tive power, through the agency of cell life or otherwise, 
in giving rise to products that do not pre-exist in the 
3 certainly the mammary. But now, as it ap- 
ra that all the constituents its secretion contains arc 
found in the blood, we can scarcely suppose that the 
does more than merely strain them out; of 
in common with all such structures, it posse — 
wlifit might aptly be termed an elective filtrating pow- 
the exudation of the iodide of potas- 
sium from the blood, but refuses a passage to the ferro- 

ide. And, finally, the conclusion wo tlms conic to 

the remark heretofore made, thai the more thor- 

■ can the system produce in an hour? 
To wlint conclusion maj 
n of the mammary gland? How d 
ral theor ion ? 



204 THE SKIN — THE RETE MUCOSUM. 

oughly we study the secretions delivered by the various 
glands, and the more perfectly we identify the sources 
from which their constituent ingredients have been de- 
rived, the more we should be disposed to impute gland- 
ular action to the physical process of elective filtration, 
and the less to the agency of cell life. 

OF THE SKIN. 

The skin is composed of two layers, the epidermis or 
cuticle, and the derma or cutis. It contains two sys- 
tems of glands, one for the removal of water, and an- 
other for that of oily substances. It also presents sub- 
sidiary parts or appendages, such as the nails and hair. 

The epidermis, or exterior portion of the skin, origin- 
ates from the cutis. It has a different thickness in dif- 
ferent parts ; the contrast, in this respect, being very 
well shown upon the soles of the feet and the eyelids. 
In this respect its use is mechanical. It serves as a pro- 
tective covering to the parts it envelops, being thick 
where pressure and hard usage have to be provided for, 
and thinner where there is a necessity for motion. It 
consists of an aggregation of nucleated particles adher- 
ing together, the deepest being granules, the intermedi- 
ate more perfect cells, which gradually become flattened 
scales as they are examined nearer the surface. They 
undergo constant exuviation, and are as constantly re- 
placed from beneath, the superficial ones becoming dry 
and horny, thus furnishing a resisting tegument. 

At one time it was supposed that the rete mucosum, 
or layer of Malpighi, which is the lowest portion of the 
cuticle, and therefore resting on the cutis, is a distinct 
structure. It is, however, merely the most recently- 
formed portion of the cuticle. The netted appearance 
it presents originates in the eminences of the papillary 
structure below. Many of its constituent particles con- 
tain coloring matter, especially in the dark races. The 
pigment seems to be produced by the agency of the 
sunlight and continued high temperature, though it dis- 
appears gradually as the cells containing it approach the 
surface. It yields a very large percentage of carbon. 

Of how many layers is the skin composed ? What is the struc- 
ture and use of the epidermis? What is the rete mucosum and its 
origin? 



THE DKHMA OR TRUE SKIN. 



205 



Beneath the epidermis is the derma or true skin. It 
is composed of fibrous tissue, which also serves to con- 
nect it with the parts beneath, blood-vessels, lymphatics, 
and nerves. In its areolar tissue both the white and 
yellow fibrous elements are found, the proportion of 
each varying according to the mechanical function the 
part has to discharge, the yellow predominating where 
elasticity is required, and the white where a resistance 
to pressure. The derma also contains organic muscular 
fibres, to which its property of corrugation, as in cutis 
anserina, is due. On different parts it is of different 
thickness, being thinnest where motion has to be pro- 
vided for. A deposit of fatty material, lodged beneath, 
gives it a yielding support. Its outer surface presents 
a papillary structure, the instrument of touch. This is 
more perfectly developed on the inner surface of the 
palm of the hand and fingers. The furrowed aspect of 
the cutis arises from this. A farther consideration of 
the mechanism and functions of the papilte is deferred 
to the description of the sense of touch. 

The photographic engraving, Fig. 73, represents a thin 
section of the epidermis of the foot of the dog. 

The general method of arrangement of the constituent 
portions of the skin may be gathered from the perpen- 



Fij. 73. 



Fig. 74. 







kin of 

lagnilled 10 dlam 

Of what ifl -in com] oeed ? T<» what is its occasional cor- 

rogati Where u the papillary structure most developed? 



206 THE SUDORIPAROUS AND SEBACEOUS GLANDS. 



dicular section of that of the external auditory meatus in 
Fig. 74 (page 205), a, the derma ; 6, rete mucosum ; c, 
horny layer of epiderma ; c?, coil of ceruminous glands ; 
6, their excretory ducts ; J\ their apertures ; </, hair-sacs ; 
A, sebaceous glands ; i, masses of fat. 

The Sudoriparous Glands originate in depressions 
of the cutis or tissues beneath, occurring in some parts, 
as in the axilla, more numerously than in others. They 
consist of a tube wound on itself, and sometimes divid- 
ing in convoluted branches. The knot thus arising is 
contained in a cell, the wall of which is copiously sup- 
plied with blood-vessels : the duct passes through the 
superjacent tissues. The tube is formed of a cylinder of 
basement membrane lined with epithelium. The base- 
ment membrane may be considered to be 
derived from the outer surface of the pa- 
pillae, and the epithelium is an external 
projection of the cuticle. The duct, on 
. its passage outward, loses its basement 
membrane as it escapes between the pa- 
pillae ; and it has a spiral or helical as- 
pect, an arrangement probably intended 
to keep the calibre open. It is estimated 
that the number of sudoriparous glands 
is about seven millions, and the total 
length of their tubing about 28 miles. 

Fig. 75 is a sudoriparous gland from 
the palm of the hand : a a, knot of tubes 
with two excretory ducts, b b, uniting 
into a helical canal, which perforates the 
epidermis at c, and opens on its surface 
at d: the gland is imbedded in fat vesi- 
cles at e e e e. 

The Sebaceous Glands are distribu- 
ted in different abundance in various 





Sudoriparous gland, 



magnified 20 diam- parts, their office being to lubricate the 
hair, to keep the skin in a flexible condi- 
tion, and avoid the inconveniences of friction. Their 
ducts open either into the hair follicles or upon the cu- 
ticular surface; the gland consisting of basement mem- 
Describe the section, Fig. 74. Describe the sudoriparous glands. 
What is the length of their tubing ? Describe Fig. 75. What is the 
office of the sebaceous glands? 



EXCRETION AND ABSORPTION BY THE SKIN. 207 

brane lined with epithelium, the cells of which, as they 
reach maturity, become filled with a sebaceous or oily 
material. The ear glands of this class secrete a waxy 
matter. 

Such being the construction of the skin, w r e have next 
to speak of its action. It discharges a double function : 
1st, as an excreting, and 2d, as an absorbing organ. In 
this respect it Iras an analogy with the raucous mem- 
brane, which, indeed, is a reflection or continuation 
of it. 

The skin permits water, saline and fatty substances, 
to escape from it in quantities differing on different por- 
tions of its surface, the nature of the secretions varying 
to meet local requirements. In the examination we are 
now entering upon, we shall speak of these substances 
and their proportions in a general way, overlooking, for 
the time, the particular variations. Yet that such vari- 
ations exist is clear on the most superficial observation. 
The sweat of the feet differs from that of the general 
surface, as, again, does that of the arm-pits. 

It has been usual to distinguish the watery transuda- 
tion into two portions, that escaping from the perspira- 
tory ducts, and that passing through the surface of the 
cuticle. It has even been said that the true glandular 
secretion passing from the ducts is not more than one 
sixth of the total cutaneous exudation ; but this, I be- 
lieve, is altogether erroneous. When we recall the im- 
permeable nature of the horny and dried scales consti- 
tuting the outer portion of the cuticle, and that these 
are constantly coated over with an oily varnish issuing 
from the sebaceous glands, we may infer that the cuta- 
-urface between the mouths of the perspiratory 
is constructed rather for the hinderance of evapo- 
ration than for its promotion ; and though the oily mat- 
ter with which the skin is thus imbued is justly regard- 
AS having for one of its functions the prevention of 
injury from the admission of external moisture, it must 
be equally effectual in stopping the escape of water from 
within. The tardy manner in which water thus escapes 
is illustrated by the operation of blisters. 

What functions doei the -kin discharge? What substances es- 
cape with the water of perspiration ? In what manner is the water 
rem< \ 



208 OF EXHALATION — OF PERSPIRATION. 

Under the form of steam, water continually escapes 
from the skin. It also, on certain occasions, issues in 
the liquid state as drops of sweat. To its escape under 
the form of steam the designation of exhalation or in- 
sensible perspiration is given ; but if under the form of 
sweat, that of sensible perspiration. 

Of Exhalation. — On condensing the vapors arising 
from the skin, they are found to consist of water con- 
taining a little acetate of ammonia. With the water 
likewise escapes carbonic acid gas. From the experi- 
ments of Valentin, the average of loss of water through 
the skin is two pounds and nearly half an ounce a day. 
Seguin's experiments would make it two pounds and 
three quarters. It has been shown in Chapter X. that 
• the action of the skin is partly meteorological : the 
amount of water passing through it depends on the 
dew-point, the atmospheric temperature, the conducti- 
bility and perviousness of the clothing. Whatever phys- 
ical circumstances promote surface evaporation corre- 
spondingly promote the action of the skin. Moreover, 
this membrane acts vicariously with the kidneys, and 
this not only as regards the water, but also as regards 
the solid matter, a large amount of which is thrown off 
in the course of the day. 

Of Perspiration. — When the atmospheric tempera- 
ture is high, and more particularly if muscular exertion 
be resorted to, the quantity of water issuing from the 
perspiratory ducts is so great that it can not be evapo- 
rated. It then exudes as drops of sweat, which become 
mingled with the oily seoretion prepared by the seba- 
ceous glands. From this commingling it is scarcely pos- 
sible to obtain the sweat, in an uncontaminated condi- 
tion, suitable for analysis, or even to exclude the detri- 
tus of the cuticle itself. In a thousand parts of sweat 
there are from five to twelve and a half parts of solid 
material. 

I have spoken of the double action of the kidney, its 
mechanism for removing saline solutions, and also that 
for combustible material. The functions of the skin are 

"What is meant by sensible and insensible perspiration respectively ? 
What estimates have been made of the quantity of water thus re- 
moved ? Why does the skin act in a variable manner? What 
quantity of solid material is found in perspiration ? 



ABSORPTION BY THE SKIN — ITS FUNCTIONS. 209 

similar. It is not a mere analogy that exists between 
the action of these organs ; the occurrence of urea and 
of the salt substances, in both secretions, is a fact of the 
utmost significance. I believe that the sudoriparous 
glands are the counterparts of the Malpighian bodies, 
and the sebaceous glands, in their function, are the coun- 
terparts of the uriniferous tubes. 

Besides exercising the functions of exhalation and per- 
spiration, numerous facts demonstrate that the skin ex- 
erts an absorbent action. The endermic application of 
remedial agents establishes this in a satisfactory manner. 
That water can find access in this way is shown by the as- 
suaging of the thirst on taking a bath ; nor is the amount 
insignificant, since it may give rise to a considerable in- 
crease of weight. Gaseous substances also find entrance 
through the skin. If the hand be put into a bell-jar con- 
taining oxygen, nitrogen, or carbonic acid at the pneu- 
matic trough, absorption of those gases ensues. Proba- 
bly it is a standard function of the skin to permit a par- 
tial arterialization of the blood, atmospheric oxygen be- 
ing exchanged for carbonic acid through it, an action 
the residual trace of the community of function between 
the skin and mucous membrane. In the case of some 
animals this cutaneous respiration is well marked. 

Recapitulating now the more important actions of the 
skin, the following statement may be made : It regu- 
lates, to a certain extent, the amount of water in the 
system, disposing of it, as the case may be; either as 
sensible or insensible transpiration. The water doubt- 
less maintains its liquid condition until it presents itself 
at the mouths of the sudoriparous ducts, moistening the 
general surface of the skin, and then being evaporated; 
or, if the supply be greater than can be thus removed, 
it accumulates as drops of sweat. There appears to be 
no substantial reason for believing that any portion of 
water transudes directly through the structure of the 
cuticle, since the scales composing it are of an impervi- 
ous and almost horny nature, and their interspaces are 
fortified against any such leakage by the oily exudations 

What is meant by the double action of the skin? What analogy 
does it bear to the action of the kidney? How may it be shown 
that the skin absorbs water? How may it be shown that it absorbs 
gases ? Give a summary of the action of the skin. 



210 DIVISIONS OF THE NERVOUS SYSTEM. 

of the sebaceous glands. With the water thus present- 
ing on the surface are many compounds which are also 
constituents of the urinary secretion. Among these, urea 
may be particularly pointed out, thus indicating a simi- 
larity of instrumental action between this organ and the 
kidneys, and this is farther substantiated by both con- 
taining provisions for the elimination and escape of the 
hydrocarbons ; but besides these direct functions there 
are other very important collateral agencies the skin ex- 
erts, and particularly as a regulator of temperature. In 
this respect the action is, to a certain extent, meteoro- , 
logical. But this has been previously treated of so much 
in detail that it is unnecessary to resume the considera- 
tion of it now. 



CHAPTER XIII. 
OE THE NERVOUS SYSTEM. 

Divisions of the Nervous System. — Cerebrospinal and 
Sympathetic. — Fibrous and Vesicidar. 

Structure and Functions of Nerve Fibres. — Centripetal 
and Centrifugal. — Rate of Conductibility. 

Anatomical Exami?iatio?i of the Structure and Func- 
tions of Nerve Vesicles. — They diffuse Influences, are 
Magazines of Force. — Element of Time introduced 
by Registering Ganglia. — Oxidation necessary to 
Nerve Activity. — Necessity of Repair and Rest. — 
Electrical Examination of the Functions of Vesicles. 
— Anatomical and Electrical Examinations agree. 

Vestiges of Impressions and their Interpretation. — Fi- 
nite Nature of Knowledge. — Mental Emotions. 

The nervous system is regarded as consisting of two 
portions, the cerebro-spinal and sympathetic. The for- 
mer is composed of the spinal cord, the brain, the nerves 
proceeding from them, and their ganglia ; the sympa- 
thetic is composed of a series of ganglia, united by inter- 
communicating threads on each side of the vertebral 
column, and supplying branches to the coats of the 

Into what portions is the nervous system divided ? 



NERVE FIBRES OR TUBES. 211 

blood-vessels and viscera of the great cavities. Both 
portions contain two kinds of structure, a fibrous and a 
vesicular. 

Of the FIBROUS there are two varieties, one belonging 
to the cerebrospinal, and the other to the sympathetic. 
The former may be described as a delicate membranous 
tube, containing a semi-fluid material, and presenting 
under the microscope a pellucid glassy appearance when 
examined in the recent state; a spontaneous separation 
or partition, however, soon ensues, a. white material or 
medulla appearing immediately within the membranous 
tube, and affording a contrast to the portions toward 
the centre or axis. In this state the nerve-tube presents 
the appearance of parallel lines toward its periphery, 
the outer one corresponding to the membranous sheath, 
and the inner to the internal limit of the coagulated ma- 
terial. In this condition the tube is very prone to as- 
sume a beaded appearance, either by the influence of 
pressure, or spontaneously. Names have been given to 
distinguish these parts from each other ; the central 
grayish portion is called the axis cylinder or axis band, 
since it may be of a flattened shape ; and the material 
surrounding it, intervening between it and the membra- 
nous investment, is designated the medulla or white sub- 
stance of Schwann. There can be no doubt that the 
membranous tube, the white substance, and the axis cyl- 
inder discharge different physiological functions. In 
chemical composition the) 7 also differ: the tube is a ni- 
trogenized structure, the white, substance oleaginous, 
and the axis cylinder is supposed to be nitrogenized 
'. In the first development, the axis cylinder is first 
formed, and the white substance then cast round it. 

If a portion of a nerve, a, Fig. lb 

/6, be placed in concen- a i 

A acetic acid, the axis 
cylinder of its included tubes 
will, in tl, Of a day or. ****** ***** 

two, be seen protruding in a brush-like form, as at&, the 

effect being very well shown when the nerve is sufli- 

What structure* do both contain? How many varieties of the 

fibrous arc tl. cribe the ceiebro-epinaL What is the ap- 

ranee ofsach a nerve-tube after death ? Where is the white sub- 
stance of Schwann? What effect is represented in Fig, 7<; ? 




212 NERVE FIBRES OR TUBES. 

ciently slender to be subsequently examined by the mi- 
croscope. 

Of fibres, arranged parallel to each other in bundles, 
the bundles united by fibro-cellular tissue, nerves are 
composed, the tissue not only accomplishing that me- 
chanical object, but also affording a nidus for blood-ves- 
sels, running in a course parallel to the nerve fibres. 
Though we have spoken of those fibres as cylinders, 
they, in reality, approach more nearly to the figure of 
acute cones, since, though their diameter is from the 
2 q^ to the ^oVu" of an inch in the nerve trunks, they di- 
minish to the 10 i 00 or the l4 ^ 00 of an inch as they 
reach the nerve centres, and, in the same manner, their 
diameter becomes less as they branch off in their periph- 
eral distribution. 

The sympathetic fibres differ from the preceding in 
appearance. Being of a yellowish-gray color, and only 
about half as large, they do not show the separation into 
an axis cylinder and white investment after death, as is 
the case with cerebro-spinal fibres ; they may therefore 
be regarded as being more homogeneous in their con- 
struction, or possessing a constitution like that of the 
other kind of fibres when they undergo diminution and 
approach their central or peripheral termination. Even 
in the cerebro-spinal fibres the quantity of white sub- 
stance present is very variable ; the retina, the olfactory 
organ, and the Pacinian corpuscles furnish instances of 
its absence. The sympathetic, gray, or gelatinous fibres, 
as they are indifferently called, contain many nucleated 
corpuscles, rendered very distinct by the action of acetic 
acid. 

Nerve fibres terminate in various ways. Their ends 
may thin out and become free, or they may form a loop, 
and so return back in their course. Each nerve runs in 
an unbroken line from its origin to its termination, but 
between the adjacent ones intercommunication is estab- 
lished by the formation of plexuses. On the other hand, 
as the fibres are preparing to enter nervous centres, the 
membranous tube dilates so as to receive a nerve vesi- 

Why may these fibres be spoken of as cones ? Describe the sym- 
pathetic fibres. What relation do they bear to the cerebro-spinal ? 
In what modes do nerve fibres terminate? In what manner are 
they attached to the vesicles ? 



NERVE VESICLES. 



213 



cle, with which the diaphanous axis cylinder is thus 
brought in contact. Where corpuscles are received 
into the membranous sheath, it is not always certain but 
that the fibre has some other termination beyond. 

The vesicular nervous substance is composed of nu- 
cleated cells, containing a granular substance, with which 
there are intermixed, especially near the nuclei, pigment 
granules. These granules, however, are sometimes ab- 
sent, as in the vertebrate. The nucleus of each gangli- 
onic vesicle often presents a nucleolus; the diameter of 
the vesicle varies from -^j to 1 } 5 of an inch. These 
vesicles are found in the nerve centres, their coloring 
material communicating to those parts the peculiar tint 
they display. In shape they vary very much, some be- 
ing spherical, some ovoid, and others caudate, exhibit- 
ing processes filled with granules, or which, becoming 
eventually transparent, communicate with similar pro- 
cesses from other cells, or are continuous with the axis 
cylinders of the nerve-tubes. The 
axis cylinder is perhaps a continua- 
tion of the nucleus of the cell. The 
ganglion vesicles, as they are term- 
ed, are characterized by containing 
a large amount of phosphorized oil, 
and it is prob- 
able that the 
oxidation of 
this material i 
is a condition 
of their func- 
tional activity. 
/. 7 7, gan- 
glion globules 
(nerve-cells), 
from the I 
s e r i a n 
glion of the 
cat. 1. ( 
with short pale 
process >lio\v- '/ **- — ^ 

, li- Hipolar mrvo-rell, magnified 

urg the origin 

1 1 icribe the compositiun of vesicular substance. What do 



k 



) 



/ lc 





214 BIPOLAR AND MULTIPOLAR NERVE-CELLS. 

of a fibre ; a, sheath of the cell and nerve-tube, contain- 
ing nuclei ; 5, cell membrane of the nerve-cell. 2. Cell, 
with the origin of a fibre without sheath; 5, cell mem- 
brane of the nerve-cell. 3. Nerve-cell, deprived, in the 
preparation of it, of its membrane and external sheath. 

Fig. 78 (page 213), bipolar nerve-cell of the pike, con- 
tinued at each end into nerve-tubes, a, sheath of the 
nerve-cell; 6, sheath of the nerve; c, medulla; d, axis 
cylinder continuous with the contents of the nerve-cell, 
6, which have shrunk away from the sheath after action 
by arsenious acid. 

Fig. 79, caudate nerve vesicle of the multiple kind : 
a, the nucleated vesicle ; &, its processes. These prob- 

Fig. 79. 




Multipolar nerve-cells, magnified 200 diameters. 

ably are continuous with the axis cylinders of the nerves, 
in connection with the vesicle. 

FUNCTIONS OF NERVE FIBRES. 

That the function of nerve fibres is to conduct impres- 
sions, is proved by many different facts. On putting a 
ligature round a nerve, or cutting it across, it no longer 
transmits the usual influences. A more critical exam- 
ination shows that impressions made on the external ex- 
tremities of a nerve are conveyed by it to the centres, 
and the influences originating in the nervous centres are 
conducted along such trunks to the parts to which they 
are distributed. This double duty therefore implies 

What are unipolar, bipolar, caudate vesicles ? What is the func- 
tion of nerve fibres ? What is the effect of a ligature or section of a 
nerve^? 



CEXTEIPETAL AND CENTRIFUGAL FIBRES. 215 

that there are two classes of fibres, the centripetal and 
centrifugal, though thus far no structural difference be- 
tween them has been detected. They can not of them- 
selves either originate impressions or motions, these in 
every instance arising from external or central agency. 
The centrifugal fibres, when cut across, may show T no ef- 
fect if the part still remaining attached to the nerve cen- 
tre is irritated ; but if the other part connected with the 
periphery be pressed upon or pinched, muscular contrac- 
tion, that is, motion, results. If centripetal fibres be ex- 
amined in like manner, the part connected with the pe- 
riphery being irritated, no result arises; but if the part 
connected with the centre be irritated, sensations, gen- 
eral or special, as the case may be, are perceived. These 
several effects ensue when the motor or sensory nerve is 
intact ; for, on irritating the one or the other, motion or 
sensation, as the case may be, is produced. If the whole 
trunk of a centripetal nerve be irritated, the mind refers 
the sensation to all those parts to which the branches* 
of that nerve are distributed ; if a part only, then the 
sensation is limited to those portions to which the fibrils 
of that part go ; but, besides this, the mind also recog- 
nizes the particular spot upon the trunk to which the ir- 
ritation has been applied. In like manner, when the en- 
tire trunk of a centrifugal nerve is irritated, all the mus- 
cles it supplies contract ; or, if only a part, then those 
muscles supplied from that part. From the anatomical 
fact that a nerve fibre does not anastomose with its 
neighbors, the influences it conveys are transmitted 
along it without any lateral diffusion, and every fibre 
discharges one duty, and one alone. The centripetal 
can never assume the function of .the centrifugal ; and 
in the case of nerves of special sense, there is the same 
restriction : the optic nerve can not transmit the impres- 
Bionc ads, nor the auditory the vibrations of light; 

the ner\ mmon sensation are affected neither by 

one or the other, but they are by variations of tempera- 
ture. The velocity with which these influences | 

ng nerve fibres is indefinitely less than that with 
which electricity moves in a metal conductor. Thus 

How many classes of fibres are there? What i> the effect <jf irri- 
tating a sen-ory <.r a motor fibre? Do nerve fibres ever di-cli.: 
more than one function? 



216 FUNCTION OF NERVE-CELLS. 

far, however, no satisfactory measure of it has been ob- 
tained. The experiments of Helmholtz give, for the 
rate of propagation, from 83 to 88 feet per second in the 
frog, and in man 200 feet, the velocity rising with the 
mean animal heat. It can not be denied that there is a 
general resemblance between the manner in which, a 
nervous fibril transmits its influences and that in which a 
conducting medium conveys an electric current, though 
the velocity may be very different. There is a resem- 
blance between the arrangement of the axis cylinder 
surrounded by its white substance and membranous 
tube, and that of a metalline wire wrapped round with 
silk, or other non-conducting material in many electrical 
arrangements. An electric current artificially transmit- 
ted along a nerve trunk will, as the nature of that trunk 
may be, give rise to muscular contraction, or produce 
general or special sensations, or originate reflex action. 
For these reasons, it has long been supposed, by many 
^physiologists, that the influence passing along nervous 
fibres is analogous to electricity, if it be not identical 
therewith; but all attempts to prove the existence of 
an electric current, either in the centripetal or centrifu- 
gal fibres, have thus far been abortive. 

FUNCTION OF NERVE-CELLS. 

The nervous fibres having for their duty the conduc- 
tion of external impressions and the transmission of 
nervous influences, the nerve-cells or vesicles are for the 
reception of those impressions and the origination of 
those influences. The nerve centres or ganglia are made 
up of vesicles, granules, and nerve-tubes conjointly. 

For the explanation of the function of the nerve cen- 
tres, it is essentially necessary that we should have clear 
views of the function of the nerve vesicles. It has ap- 
peared to me that their duty is manifested by their ana- 
tomical relations. The influence, whatever it may be, 
passing along a nervous cord, is completely isolated 
therein, and never leaves the fibril in which it is passing 
from its origin to its termination. It is isolated by the 

What is the rate of conduction in nerves? What resemblance is 
there between nerve conduction and electric conduction ? What are 
the functions of nerve-cells ? What conclusion is to be drawn from 
the anatomical construction of nerve vesicles ? 



TESICLES ARE MAGAZINES OF FORCE. 217 

white substance of Schwann. But it is very plain, as 
many phenomena of the nervous system prove, that (here 
are places of escape for this influence, although it may 
be confined in the nerve fibre, and these places can be 
no other than the vesicles. Their caudate aspect, or 
multipolar form, as it is often termed, will bear no other 
interpretation. The disturbing influence, coming along 
the axis cylinder of a nerve tibre, finds itself delivered 
into the granular material in the interior of a vesicle, a 
material physically continuous, in the opinion of many 
physiologists, with the structure of the axis cylinder. 
Through this granular material the influence is trans- 
mitted, and if the vesicle should have on its distant con- 
tour two or more nerve fibres connected with it, it 
would seem to be the necessary result of such a state of 
things that the influence will pass down all those chan- 
nels. For these reasons I regard the nerve vesicles as 
being constructions for the purpose of opening out the 
closed nerve fibres, and permitting them to deliver^their 
energy into new tracks. 

But more than this. Whatever may be the principle 
by which the nervous influence is propagated, or con- 
ducted from point to point of the granular material 
within the vesicle, there must be now, since there is no 
structure to prevent it, a lateral spreading of effect. It 
is not to be supposed that the passage is made in a di- 
rect line, from the terminus of the centripetal to the 
origin of the centrifugal fibre, across these caudate ves- 
icles, and restricted thereto. There is no isolator to 
confine it in any such track, and it seems to follow of 
v that the whole contents of the vesicle must be 
affected, and this irrespective of its magnitude. Such a 
tdition of things introduces the suspicion of a second 
at duty the vesicles may discharge in retaining with- 
in then entfl for a short period, the influ- 
9caped laterally, and thus they be- 
ne temporary magazines of power. And perhaps this 
may be the true interpretation of the action of unipolar 
and bipolar 9; the unipolar being a capsule for 
the collection and conservation of the entire delivered 

are they plated in fanction to neire-cells ? Why must dif- 
grannlar material take place? What u the fanction 
- f unipolar and bipolar ?e» I 

K 



218 FUNCTIONS OF VESICLES. 

influence, the bipolar to admit of the passage onward 
of a large portion of the force, but by lateral diffusion 
to preserve or delay a part, and the multipolar at once 
permitting of conservation and of a discharge into, per- 
haps, a multitude of new channels. 

Upon the same principle that multicaudate vesicles 
permit of the escape of nervous influence from the sin- 
gle channel in which it has been coming into many new 
ways, so likewise they must be the seats of the interfer- 
ence of influences delivered into them from many centrip- 
etal fibres at the same time. Thus we may imagine a 
tricaudate vesicle into the granular material of which an 
influence is delivered simultaneously by two centripetal 
fibrils, and these, reacting on one another in the interior 
of the vesicle, give rise to a resultant differing from 
them both, and this is passed on through the third, the 
centrifugal fibril. 

Regarded in this way, the function of a nerve vesicle 
may*therefore be stated to be, 1st. To permit the escape 
of an entering influence out of the solitary channel in 
which it has been isolated into any number of diverging 
tracts ; 2d. To combine influences entering it from va- 
rious directions into a common or new result; 3d. By 
permitting of lateral diffusion to take off and keep in 
store for a certain duration a part of the passing in- 
fluence. 

Our attention can not fail to be arrested by this last 
effect ; for if there be a property characteristic of the 
nervous mechanism in its utmost degree of development, 
it is this of retaining the relics or traces of impressions 
formerly made upon it. As it goes on increasing in 
complexity as we rise through the animal series, the pro- 
vision for the retention of such impressions becomes 
more and more strikingly marked. Ganglionic masses, 
which, from their position and structure, are marked out 
for this duty, appear in that ascending scale in increas- 
ing magnitude. To these we may aptly apply the des- 
ignation of registering ganglia, since they truly store up 
the traces of ancient impressions and keep them in re- 
serve. These ganglia must, moreover, be the scenes of 

How is it that interference of influences may take place ? What 
are the three chief functions of vesicles? What are registering gan- 
glia? 



HOW NERVE CENTRES ACT. 219 

the interaction and interference of the impressions they 
thus contain. 

The registering ganglia thus introduce the element of 
time into the action of the nervous mechanism. The 
impression which without them would have forthwith 
ended in action is delayed for a season, nay, perhaps 
even as long, though it may be in a declining way, as 
the structure itself endures ; and with the introduction 
of this condition of duration come all those important 
effects ensuing from the various action of many received 
impressions, old and new, upon one another. 

The action of every ganglionic mechanism depends 
upon the existence of certain physical conditions, among 
which, as being of paramount importance, one may be 
discerned. It is the due supply of arterialized blood. 
If this be stopped but for a moment, the nerve mechan- 
ism loses its power, or if diminished, the display of its 
characteristic phenomena correspondingly declines. If, 
on the contrary, the supply be unduly great, or its oxi- 
dizing power artificially increased, there is a more ener- 
getic action. This latter condition of things is present- 
ed in the earlier stages of the respiration of protoxide 
of nitrogen, an increased muscular power, and an exag- 
geration of the processes of intellection. The opposite 
state is witnessed when carbonic acid, more or less di- 
lute, is breathed, from that blunting of the intellectual 
faculties and indisposition for muscular exertion felt in 
ill-ventilated apartments where carbonic acid is permit- 
ted to accumulate, to the profound torpor and insensi- 
bility experienced when it is in a more concentrated 
state. These exaltations and depressions of the capa- 
bilities of the nervous instrument are, therefore, clearly 
of a chemical kind, and may be produced artificially and 
at pleasure by the respiration of appropriate gases or 
the ad ministration of certain drugs. Nay, even the ac- 
nilations of the effete products of the economy are 
sufficient to give rise to such diminutions of power, as 
we see when bile or urea is permitted to accumulate in 
the blood. The therapeutical and toxicological influ- 
ences of certain medicaments are illustrations ofth< 

<lo they introduce the element of time? Under what condi- 
tion do nenre centr What ensues vrhen protoxide ofnitn 
ireathed? What vrhen carbonic acid? 



220 WASTE AND REPAIR OF NERVOUS MATTEK. 

principles. Of such substances, some act on the senso- 
rial and some on the motor powers. 

The copious distribution of arterial blood to the nerv- 
ous centres indicates that they undergo a rapid w&ste. 
That supply can not be for the mere purposes of growth 
alone, since, when once maturity is reached, the nervous 
mechanism presents but little expansion. The provision 
for nutrition assures us that that action must be rapidly 
going on ; but the equilibrium of the system betrays 
that such nutrition is not for development, but for the 
repair of waste ; and, indeed, this waste proceeds at 
such a rate that there arises in some portions of this 
system a necessity for periodic repose or sleep, a time 
for the restoration of the parts. If any arguments were 
required to establish beyond dispute that such a disin- 
tegration of the material of the nerve centres does oc- 
cur, it w r ould be furnished by an examination of the 
urine ; for, in nervous substance, phosphorus occurring 
as a characteristic ingredient, it must give rise to the 
production of phosphoric acid, or salts thereof, in the 
supposed periods of activity. Moreover, in this meta- 
morphosis of the vesicular structure ammonia must 
eventually arise, from the cell walls if from no other 
source, and accordingly we find in the urine that char- 
acteristic double salt, the phosphate of soda and ammo- 
nia. The amount of these alkaline phosphates has long 
been known to be in proportion to the activity of the 
nervous system, particularly in the case of individuals, 
as clergymen, w r hose mental powers are taxed unduly at 
stated intervals. The general fact that the degree of 
energy this system exhibits is dependent on the activity 
of respiration in different tribes of life might be estab- 
lished from many familiar instances. 

Vesicular nervous material contains much less fatty 
matter than the fibrous, but much more water. From 
this it would appear that' the presence of fat in nervous 
material is functionally connected with its property of 
conduction or transmission of nervous influence. Every 
thing seems to indicate that Schwann's white fatty 

How is it that the necessity of rest or sleep arises ? How is it 
known that the destruction of nerve material is proportional to its 
activity? What difference in composition is there between vesicu- 
lar and fibrous substances ? 



CIIOLESTEEINE AND PHOSPHORUS. 221 

substance only discharges the physical duty of an iso- 
lator. 

Our attention may next be directed to the methods 
of repair of the vesicular structures. Their waste, as 
just established, implies their repair. Here, as in the 
muscular tissues, the blood-vessels conduct both opera- 
tions, and the mode of distribution of the capillaries is 
such as to bring the circulating current into the most 
favorable position for discharging this duty. The vesi- 
cles are included in the midst of a network of capilla- 
ries, and it is believed that there is a resemblance be- 
tween their mode of growth and that of the cells of the 
epidermis — that is to say, they arise from nuclei on the 
spaces nearest to the supply of blood, and gradually un- 
dergo development as they prepare for connection with 
the tubular tissue, assuming the place of cells that have 
discharged their function and are undergoing disinte- 
gration. This gradual passing onward and wearing 
away recalls the changes in the structure of the cuticle. 

To two of the substances thus met with in these ex- 
aminations of the nervous system our attention may be 
directed. These are cholesterine and phosphorus. Of 
the former we can not have failed to remark that it is a 
constant ingredient in the product of the action of the 
liver. It is a lipoid, and is found in biliary calculi ; and 
though it may be regarded in one sense as an excremen- 
titious body, since it occurs in fa?cal matter, yet it also 
appears as a normal constituent of the blood. It may 
therefore be inferred, if the opinion of its existence in 
the white substance of Schwann be correct, that it is one 
among the various functions of the liver to prepare this 
y. Of phosphorus, it might be said that it, among 
the chemical elements, is most strikingly characterized 
in its ac te by the intensity of its affinity for oxy- 

I >n this depends its quality of shining in the dark, 
which has given it a name; but by many 
h, for example, as exposure to a particular 
1 especially to the light of the sun, it 
may be thrown into a con. lit inn so completely passive 

• fa tli«- function of the white substance of Schwann? In 
what manner are thr* nerve 1? Whal analogy < ; 

:,in ? What is chol In what 

two bi pboe] horns occur? 



222 volkma^n's electrical experiments. 

that its chemical energies almost disappear. The doc- 
trine that was presented in explanation of the destruc- 
tion of one part of the system by the air introduced by 
respiration while another is protected therefrom, as de- 
pendent on the allotropic condition of those parts, is 
presented here again in discussing the destruction and 
repair of the nervous tissue ; for it is only when it is 
ready to be removed that the phosphorized constituent 
assumes the active state, and in so doing gives rise to 
the development of force. On this view, it would ap- 
pear that such phosphorized compounds are obtained 
from the vegetable kingdom in the food in a passive 
state, the tissues of plants having deoxidized them un- 
der the influence of the sunlight, which simultaneously 
has thrown them into the condition of inactivity, and 
perhaps it is the assumption of that very condition that 
is the fundamental cau^e of their deoxidation. 

By the aid of the conclusions we have come to re- 
specting the function of nerve-tubes and vesicles, as 
shown by their anatomical structure, we shall not have 
much difficulty in explaining the offices of nervous arcs. 
The results at which Ave thus arrive, from a considera- 
tion of those cells, are singularly fortified by the electric- 
al experiments of Galvani, Volta, Nobili, and especially 
those of Volkmann. Among these, the three following 
are of primary importance : 

1st. When a continuous electrical current is passed 
along a centrifugal nerve, contraction of the muscles 
which that nerve supplies takes place, and continues as 
long as the electric current passes, without relaxation, 
but ceases the moment the current is stopped. 

2d. When a continuous electric current is passed 
through a ganglion, contraction of the muscles supplied 
by the centrifugal nerves of that ganglion ensues. These 
contractions do not alternate with relaxation, and on 
stopping the current the contraction does not cease, as 
in the preceding case, but is continued for a period of 
time. 

3d. When a continuous electric current is passed 
down a centripetal nerve, muscular contraction of the 

How is it that phosphorus is deoxidized in plants? What three 
results may be witnessed on passing an electric current through 
nerves ? 



DEDUCTIONS THEREFROM. 228 

parts supplied by the corresponding centrifugal nerves 
occurs, and the/e contractions alternate with relaxations. 

Iu view of these facts, we are brought to two conclu- 
sions : First, that there is a property in the ganglion, 
enabling it to hold in reserve a portion of the influence 
brought into it, so as to keep up the action for a period 
of time after the original disturbing causes have ceased. 
Second, that* the structure of the ganglion is such as to 
permit the escape of the coming influence by lateral 
ways, either periodically or otherwise, and so to pro- 
duce from a continuous influence an intermitting effect. 

Recalling the fact that a ganglion is made up of nerve- 
tubes and vesicles conjointly, these electrical results must 
find their solution in the elementary structure of the gan- 
glion — that is to say, in its vesicular portion ; for it is 
not to be supposed that a current of electricity, such as 
we are here considering, would ever have an opportu- 
nity of escaping from the axis cylinder along which it 
passes. The isolating quality of the white cylinder of 
Schwann would prevent any such effect. It is not nec- 
essary that we should embarrass ourselves here with the 
fact that electric currents of sufficient intensity could 
make their way out from the interior channel in spite of 
its insulating investiture, since it is only with those of a 
far less power that we have to deal. Arrived in the 
vesicle, the current at once diffuses itself throughout the 
granular material, just in the same manner that it would 
diffuse throughout a spherical conducting mass if brought 
to it by a wire, and escape therefrom through any num- 
ber of similar wires that might chance to be in contact 
with the conducting mass beyond ; and though the main 
body of the current would, as may be readily proved, 
under these circumstances move in a direct line from 
the point of entry to the point of exit, there would be, 
nevertheless, a diffusion of part of it through the con- 
ducting mass, no portion thereof remaining unaffected. 
In a good conductor, such as a metal, this laterally di- 
g current would instantly escape, but the case be- 
comes very different in the less perfectly conducting 
material, the granular substance within the cell. As in 
the secondary piles of Rit^er, which, when brought into 

What deductions have been made from such experiments ? In 
what manner does diffusion in the vesicle take pli 



224 VESTIGES OF GANGLIONIC IMPRESSIONS. 

contact with an active voltaic circle, participate in all its 
qualities, physiological and chemical, give shocks, pro- 
duce decompositions, and continue to do so for a time 
after the original influence has ceased, so a similar con- 
servation occurs in the interior of the vesicle ; and this 
I consider to be the consequence of the diiference of 
structure of the fibrous axis cylinder and the granular 
vesicle contents. The continuous lines along which the 
influence has been coming terminate on reaching the 
vesicle, and are replaced by a divided and inferior con- 
veying structure, a structure which recalls at once the 
secondary piles of Ritter just alluded to. 

As respects absorbed or registered impressions, a few 
remarks may be here made. There can not be a doubt, 
that the registry of impressions involves an actual struc- 
tural change in the ganglion, which is of a permanent 
character. These changes may be rudely and imper- 
fectly illustrated by experiments, such as I published 
years ago, of which the following may be taken as ex- 
amples: If, on a cold, polished piece of metal, any ob- 
ject, as a wafer, is laid, and the metal then be breathed 
upon, and, when the moisture has had time to disappear, 
the wafer be thrown off, though now upon the polished 
surface the most critical inspection can discover no trace 
of any form, if we breathe upon it a spectral figure of 
the wafer comes into view, and this may be done again 
and again. Nay, even more; if the polished metal be 
carefully put aside where nothing can deteriorate its 
surface, and be so kept for many months (I have wit- 
nessed it even after a year), on breathing again upon it, 
the shadowy form emerges; or, if a sheet of .paper on 
which a key or other object is laid be carried for a few 
moments into the sunshine, and then instantaneously 
viewed in the dark, the key being simultaneously re- 
moved, a fading spectre of the key on the paper will be 
seen ; and if the paper be put away where nothing can 
disturb it, and so kept for many months, at the end 
thereof, if it be carried into a dark place and laid on a 
piece of hot metal, the spectre of the key will come 
forth. In the case of bodies more highly phosphores- 

What physical contrivance do vesicles in their action resemble ? 
How may invisible impressions be made visible on metallic surfaces ? 
How long will such impressions continue ? 



IXTEUFUETATION OF SUCH VESTIGES. 225 

cent than paper, the spectres of many different objects 
which may have been in succession laid originally there- 
upon will, on warming, emerge in their proper order. 

I introduce these illustrations for the purpose of show- 
ing how trivial are the impressions which may be thus 
registered and preserved. Indeed, I believe that a shad- 
ow never falls upon a wall without leaving thereupon its 
permanent trace — a trace that might be made visible by 
resorting to proper processes. All kinds of photograph- 
ic drawing are in their degree examples of the kind. Of 
the moral consequences of such facts it is not my object 
here to speak. The world would be none the worse if 
every secret action might thus be made plain. But if 
on such inorganic surfaces impressions may in this way 
be preserved, how much more likely is it that the same 
thing occurs in the purposely -constituted ganglion! 
Xot that there is any necessary coincidence between an 
external form and its ganglionic impression any more 
than there is between the letters of a message delivered 
in a telegraph office and the signals the telegraph gives 
to the distant station, yet these signals are easily retrans- 
lated into the original words — no more than there is be- 
tween the letters of a printed page and the acts or scenes 
they may chance to describe, but those letters call up 
with clearness in the mind of the reader the events and 
scenes. Indeed, the quickness with which the mind in- 
terprets such traces or impressions in its registering 
ganglia is illustrated by the rapidity with which we 
gather the sense of a printed page without individualiz- 
ing each of the letters it contains, or as a skillful account- 
ant runs his eye over a long column of figures, and seems 
to come by intuition at once to the correct sum. 

From the preceding considerations we may infer that 
there is a necessary limitation of the amount of impres- 
sions capable of being registered in the organism, and 
therefore, in this regard, all human knowledge is finite. 
Yet its term is much farther off than might atfirst sight 
appear. A library of a given size may only be able to 
contain a given number of books upon its shelves, but 
the amount of information it is capable of containing 

What may be illustrated by phosphorescent surfaces? Illustrate 
the manner in which impressions may be interpreted. Why may it 
be inferred that human knowledge is finite? 

K 2 



226 SPONTANEOUS FUNCTIONS OF GANGLIA. 

may be made to vary with. the condensation and perspi- 
cuity of the books. 

In the hypothetical language of physiology, the nerv- 
ous centres are spoken of as the origin of the nervous 
influence or force. A close examination of the phenom- 
ena they display leads us, however, to receive such a 
statement with a certain amount of limitation. Most 
of the ganglia produce no motor impulses except under 
the actibn of external impression. Indeed, the cases in 
which the nervous centres seem to display the quality 
of spontaneously originating force are so few, and in 
their nature so doubtful, that we are almost entitled to 
disregard them. For example, the ganglia of the heart 
are by some supposed to cause, by their own inherent 
power, the contractions of that organ, which in cold- 
blooded animals, long after it has been excised, will con- 
tinue its rhythmic motions. But it is far more agreeable 
to the analogies of the nervous system to regard these 
cardiac ganglia, not as originators of power, but as mere- 
ly depositories, reservoirs, or magazines of it. There is 
nothing more extraordinary in their ability to keep up 
the motions of the organ they are connected with than 
there is in the subsidiary spring of a chronometer, main- 
taining the movement of that instrument for the period 
during which the action of the mainspring is taken off 
while it is being wound up. Yet the mainspring, and 
the subsidiary spring too, derive their mechanical power 
originally from the force which has wound up the chro- 
nometer. In this particular of the storing up of power 
for its utilization in the time of need, the whole gangli- 
onic or sympathetic system of nerves may be taken as 
the great example. 

What conclusions do we come to respecting the spontaneous func- 
tions of ganglia ? What may be remarked respecting the ganglia 
of the heart ? What mechanical contrivance do they resemble in 
their action ? 



THE NERVOUS SYSTEM. 227 



CHAPTER XIV. 

THE NERVOUS SYSTEM— Continued. 

The Spinal Cord: its Structure and Functions. — BelTs 
Discovery. — Reflex Action. — Tlie Medulla Oblonga- 
ta. — The Pons Varolii. 

The Brain: its Structure. — Sensorium. — The Cerebel- 
lum : its Structure and Functions. — Symmetrical 
Doubleness of the Brain. — Double Thought. — Alter- 
nate Thought. — Castle-building. — Sentiment of Pre* 
existence. 

The Cranial Nerves : their Functions. 

The Great Sympathetic: its Anatomy. — Relation to 
the Pneumo gastric. — Connection ivith the Spinal Sys- 
tem. — Its Ganglia. — They are Reservoirs of Force. 
— Summary of Functions of the Sympathetic. 

"We now commence a more detailed examination of 
the nervous system. This will therefore lead us to 
speak in succession of the spinal cord and medulla ob- 
longata, of the sensory ganglia, of the cerebellum and 
cerebrum, of the nerves generally, and, lastly, of the sym- 
pathetic system. 

THE SPINAL CORD. 

The spinal cord is placed in the midst of the vertebral 
canal. In form it is cylindroid, its section being ellip- 
tical, the lateral diameter being the long one. Longi- 
tudinally it has two enlargements, one about its upper 
third, the other toward its termination. Exteriorly it is 
white, but its section shows a gray substance, arranged 
in the form of two crescents connected by an isthmus. 
Above, it is continuous with the brain, which, indeed, is 
a development upon it, and below it terminates at the 
cauda equina. Its relative length is much greater in 
foetal life, at the third month of which it extends into 
the sacrum. In adult life it only occupies about the up- 

What are the chief general divisions of the nervous system? De- 
scribe the construction and position of the spinal cord. 



228 STRUCTURE OF THE SPINAL CORD. 

per two third^ of the vertebral canal ; it is generally 
stated that its termination is about the first or second 
lumbar vertebra. Moreover, it does not fill the verte- 
bral canal, being, by reason of the transverse dimensions 
of that cavity, rather suspended in than confined by it. 
The rest of the space, amounting to about one third, is 
occupied by the roots of the nerves, ligaments, the in- 
vestitures of the cord, Wood-vessels, and a liquid. 

With respect to the interior constitution of the cord, 
it is composed exteriorly of white, and interiorly of gray 
material. 

The spinal cord is surrounded by three membranes, 
continuous with those of the cranium ; the dura mater, 
the arachnoid, and the pia mater. The latter embraces 
the cord so closely as to exert a compression upon it. 
This is shown on slightly wounding it, when the white 
substance protrudes through the orifice. 

From the cord there arise thirty-one pairs of nerves, 
each nerve having two roots, an anterior or motor, and 
a posterior or sensory. 

The anterior roots issue from the anterior furrow, the 
posterior from the posterior furrow, w T here the gray sub- 
stance emerges. Of the two the latter are the larger, and 
have more radicles. They also have, in the interverte- 
bral foramen, a ganglion. Beyond the ganglion the two 
roots coalesce, and the resulting nerve trunk, passing 
through the intervertebral foramen, divides into an ante- 
rior and posterior branch, for the anterior and posterior 
portions of the body. To this general description there 
are, however, some exceptions. Thus the posterior root 
of the first cervical nerve is smaller than the anterior, 
and very often it has no ganglion. The spinal nerves 
are enumerated as eight cervical, twelve dorsal, five lum- 
bar, and six sacral pairs. 

The white or fibrous portion of the spinal cord is com- 
posed in part of the spinal nerve fibres and in part of 
commissural ones. At one time it was supposed. that 
every one of the preceding continued uninterruptedly 

Does the spinal cord fill the entire cavity of the vertebral canal ? 
How are its gray and white constituents arranged respectively? 
What membranes surround it ? How many pairs of nerves arise 
from it ? How many roots have each ? What are their functions ? 
Of what is the fibrous portion of the cord composed ? 



ITS FUNCTIONS. 229 

to the brain. On this point, however, the weight of evi- 
dence leads us to infer that the vertical distance through 
which these fibres pass is not very great, and that they 
are soon brought in connection with the interior vesicu- 
lar substance. If all the fibres passed uninterruptedly 
to the brain, we should expect that the cord would in- 
crease in thickness by a regular progression upward ; 
but this is not the case. Its enlargements correspond 
to the number of nerve roots given off from the locali- 
ties in which they occur. 

The determination of the functions of the roots of the 
spinal nerves by Bell is one of the great discoveries of 
physiology, and furnishes a solid foundation for an ex- 
act knowledge of the functions of the nervous system. 
The evidence of the truth of the doctrine that the ante- 
rior roots of these nerves are motor and the posterior 
sensory, is complete. Thus, if the anterior root of one 
of these nerves be divided, all those parts supplied by 
that nerve will exhibit loss of motion, though their sen- 
sation is unimpaired ; if the posterior root be divided, 
the sensibility of the parts is lost, though the power of 
motion is unaffected. Similar evidence may also be ob- 
tained by irritating the ends of the divided roots, mus- 
cular motion or pain, as the case may be, being corre- 
spondingly observed. 

The spinal cord transmits impressions from the pe- 
riphery to the brain, and conversely enables the brain 
to bring into action the motor nerves. Division of it 
at once causes an interruption of voluntary motion and 
Bation in those parts supplied by nerves below the 
place of the operation, the functions of the parts above 
remaining unimpaired. But, though the influence of 
the brain in exciting voluntary motion, and its capabil- 
ity of receiving sensations, is thus cut off, the severed 
portion of the cord still possesses an automatic power. 

This transmission of influences upward or downward 

doubtless, to a considerable degree, accomplished 

through the vesicular substance, the quality of which, 

in this respect, has been explained in the preceding 

chapter. But, beside! this, the exterior fibrous struc- 

How have the functions of the spinal nerve roots been determ- 
ined ? How are the cord and the brain respectively related to each 
other? 



230 BROWN-SEQUARD ON ITS CONDUCTION. 

tures possess a like function, correspondingly as they 
are connected with the motor or sensory roots of the 
nerves, the anterior columns being motor, and the pos- 
terior apparently sensory. 

The spinal cord not only permits the passage of influ- 
ences in its longitudinal, but also in its transverse direc- 
tion. This is what might be Anticipated from the struc- 
ture and functions of the cells of its gray interior. If 
the cord be cut half through in a given place, and again 
be cut half through on the opposite side, at a little dis- 
tance above or below, impressions may be conducted 
through the intermediate portion, the vesicular material 
being then their only channel. 

In a memoir on the distribution of the fibres of the 
sensitive roots, and on the transmission of impressions 
in the spinal cord, Dr. Brown-Sequard, referring to the 
two theories entertained at present — 1st. That sensitive 
impressions reaching the cord pass in totality to the 
brain along the posterior columns ; 2d. That such im- 
pressions so arriving pass directly to the central gray 
substance, which transmits them upward — offers reasons 
for supposing that both these theories, and especially 
the first, are contradicted by facts. 

It is his opinion that sensitive impressions reaching 
the cord pass in different directions, some ascending, 
others descending, but both going in part by the poste- 
rior columns, and in part by the posterior gray horns, 
and perhaps by the lateral columns, to penetrate, after 
a -short distance, the gray central substance by which, 
or in which, they are transmitted to the brain. 

The translation of impressions brought along the cen- 
tripetal fibres into motions, the exciting influence of 
which is conveyed along the centrifugal fibres, includes 
what is understood as the reflex action of the spinal cord 
as developed by Dr. Hall. Its essential condition is its 
independence of the*agency of the brain, and therefore 
unconscious nature. As general examples may be men- 
tioned, the movements that occur in swallowing ; for aft- 

Which are the motor, and which the sejtsory columns of the cord? 
"What is meant by transverse transmission in the cord? What are 
the conclusions of Dr. Brown-Sequard as respects the conduction of 
the cord ? What is meant by reflex action ? Give instances of the 
reflex action of the cord. 



ACTION OF THE CORD AND BRAIN. 231 

or the food has been carried by voluntary action into the 
fauces, its passage onward to the stomach is perfectly in- 
voluntary. In like manner, the introduction of air into 
the lungs in ordinary respiration is involuntary; for 
though it may be, to a certain extent, under the control 
of the will, yet that extent is limited, an uncontrollable 
necessity for the motion presently arising. The action 
of the valvular arrangements at the cardiac and pyloric 
oritices of the stomach, and the constant contraction of 
the sphincter ani, are farther illustrations. To these may 
be added those impulsive movements we instinctively 
make on the approach of danger or in the act of falling, 
and perhaps, too, automatic walking, as we go from place 
to place in a state of mental abstraction, paying no at- 
tention to the course we take. 

As above stated, this reflex function of the cord is in- 
dependent of the brain, though the brain can control it, 
and this the more perfectly the higher the organization 
of the animal. Breathing can go on, whether we pay at- 
tention to it or not, but we can arrest it if we choose for 
a time. 

In a general way, there is not much difficulty in dis- 
tinguishing between simple actions of the cord and those 
in which the brain is participating. In the former, no 
weariness or fatigue is ever experienced ; in the latter it 
is ; and perhaps, even in these last, involving voluntary 
muscular action, though the control is to be attributed to 
the brain, the source of the force is in the cord. 

From the facts presented by the lower animals, it mciy 
be inferred that the spinal cord does not act as a single 

_ in, but rather should be regarded as a collection of 
ganglia, special duties being discharged by special parts 
of it. 

If the view that has been presented respecting the con- 
tinuation of fibres from the cord to the brain be correct, 
these fibres discharge a commissural duty. This would 
lead us to suppose that there is a correspondence be- 
tween the functions of the columns of the cord and those 
of the roots of the Bpina] nerves, the anterior columns 

What b their essentia] condition? How may cerebral and spinal 
action be distinguished? Does the cord act as a single organ or as 

a collection of ganglia? What correspondence is there between the 
columns of the cord and the roots of its nerves? 



232 THE MEDULLA OBLONGATA. 

being motiferous, or in unison with the motor root of 
the nerves, the posterior being sensiferous, or in unison 
with the sensory root of the nerves. 

From the point of view thus presented the action of 
the spinal cord is therefore simple, or it is disturbed by 
the agency of the brain ; in the first case it offers itself 
purely as an automatic instrument ; in the latter, its com- 
missural connections with the brain make a compound 
apparatus. The former state is closely represented in* 
the construction of the amphioxus, the nervous system 
of which has no rudiment of a cerebrum or cerebellum ; 
in this animal, therefore, since also the sensory ganglia 
are merely in a rudimentary state, the mode of life must 
be purely mechanical, just as it is with an artificial au- 
tomaton, of which, when a given spring is touched, a 
given motion is made. Even among the highest verte- 
brated animals, man himself at the periodic times of qui- 
escence of the cerebrum, as in sleep, when the cerebral 
influence over other portions is, to a certain extent, sus- 
pended, an approach to a similar condition occurs ; but 
in periods of activity of the cerebrum, it can hold the spi- 
nal cord in check, controlling, and in some cases arrest- 
ing its action, and this is done through influences propa- 
gated along the structures of the posterior and anterior 
columns, which therefore are to be regarded, in this re- 
spect, as commissures to the brain. 

THE MEDULLA OBLONGATA. 

The medulla oblongata is a conical body, between the 
spinal cord and the brain. It is generally understood to 
be bounded at its upper portion by the pons varolii, but 
this is not a true limit, since its structure extends through 
the pons varolii to the crura of the brain. There is the 
same indefiniteness of limit as respects its lower bound- 
ary, which is generally said to be marked by some de- 
cussating fibres appearing on its front. Like the spinal 
cord, it has an anterior and posterior fissure, dividing it 
into two symmetrical lateral halves ; the former is a con- 
tinuation of the anterior spinal fissure, the latter of the 
posterior, and ends in the calamus scriptorius above. 

State what are the general functions of the cord. What is the 
position and structure of the medulla oblongata? 



ITS RELATIONS TO RESPIRATION. 233 

The lateral halves thus produced are marked by three 
grooves, producing four eminences, passing under the 
following names: 1st. The anterior pyramids ; 2d. The 
olivary bodies ; 3d. The restiform bodies ; 4th. The pos- 
terior pyramids. The anterior fissure is crossed about 
an inch below the pons varolii by decussating fibres, and 
hence injuries on one side of the brain produce nervous 
effects on the opposite side of the body. 

Viewed as a superposed continuation of the spinal 
cord, the medulla oblongata is the tract of communica- 
tion between that organ and the brain: the anterior 
pyramids and olivary tracts convey motor influences, 
and the restiform tracts and posterior pyramids sensa- 
tions. By experiments similar to those performed upon 
the cord, these conclusions have been maintained. 

But, besides this function of conduction, the medulla 
oblongata discharges a most important duty as a nerv- 
ous centre ; on it depend respiration and deglutition. 
The brain may be wholly removed above, and the spinal 
cord below, as far as the origin of the phrenic nerve, 
without death necessarily ensuing, but on wounding the 
medulla oblongata, the muscular movements necessary 
for the introduction of air are necessarily stopped. 

Moreover, the medulla oblongata exhibits the proper- 
ty of reflex action. So far as the^function of respiration 
is concerned, its chief centripetal nerve is the pneumo- 
gastric, but the power it possesses is participated in by 
many others, perhaps by reason of the venous condition 
into which the blood is brought from want of proper 
aeration. The violent respiratory movements by the 
sudden application of cold to the skin, the shower-bath, 
or dashing cold water on the face, are converted by it 
into respiratory muscular motions. From it also arise 
the movements required in the act of deglutition. 

Under this view of the functions of the medulla ob- 
longata, it is to be regarded as an exclusively automatic 
instrument, which can continue its operation after the 
excision of the brain. As with the spinal cord, so with 
it : its simple action may continue though its commis- 

What are the functions of the medulla oblongata? What rela- 
tions does it bear to respiration and deglutition? Give some in- 
stances of its reflex action. What relation does h< action bear to 
thr.se of the brain '■ 



234 THE PONS VAROLII — THE BRAIN. 

sural action has ceased, and this either through condi- 
tions of disease or by the administration of drugs. In 
lesions of the brain respiration may still continue, as it 
may also when sensation and voluntary motion have 
been arrested by the breathing of chloroform. 

THE PONS VAROLII. 

The pons varolii consists of a loop of fibres passing 
from one crus cerebelli to the other, around the tracts 
of communication between the cord and the brain. 
That they constitute mainly a commissure for the cere- 
bellum is apparent from the circumstance that, in those 
animals which have the median cerebellar lobe only, 
there is no pons, and in other cases its relative magni- 
tude is in proportion to the size of the cerebellar hem- 
ispheres. 

The functions of the pons varolii are therefore two- 
fold : it acts as a conductor, and also as a nerve centre. 
In the first respect, it is the channel from the spinal 
column to the cerebrum and cerebellum, and also be- 
tween the cerebellar halves, and experiments upon it, in 
giving rise to sensations and motions, are in conformity 
with what we should anticipate from the structure and 
functions of the spinal cord. 

In the second respect, as a nervous centre — when the 
cerebrum and cerebellum are removed, but the pons left 
untouched, an animal gives, tokens of sensation when 
pinched or irritated, and likewise executes motions hav- 
ing an object; these, however, are no longer observed 
after the removal of the pons. 

THE BRAIN. 

The cerebrum and cerebellum, being organs addition- 
al to the spinal cord, and developed upon it, the cord 
being able to discharge its own functions independently 
of them, we shall find it at once the most natural and 
most commodious method to consider their structures 
as arising out of its structure, and their functions as 
having relation to its functions. 

A general idea of the structure of the brain as an ap- 

Describe the position and structure of the pons varolii. What are 
its functions ? 



THE BRAIX. 235 

pendage to the spinal cord may be gathered by con- 
sidering that a bifurcation of the fibres takes place in 
the medulla oblongata, and upon one of the resulting 
bundles, the crus cerebri, the cerebrum is formed, on the 
other the cerebellum. The crus cerebri is thus com- 
posed of three strands : an inferior, the fibres of which 
have come from the anterior pyramids, and in part from 
the olivary bodies. This strand ends in the corpus 
striatum, its fibres not, however, blending abruptly with 
the vesicular matter, but passing into it in bundles. It 
is essentially motor. A superior, derived from the pos- 
terior pyramids, and terminating in the thalamus. It is 
ntially sensory. Between these, constituting the 
third portion — strand it can scarcely with propriety be 
called — is a layer of dark vesicular material, the locus 
niger. It is to be understood that the motor strands of 
the opposite sides decussate in the medulla oblongata; 
the sensory strands decussate in the mesocephalon. 

The other bundle, arising in the original bifurcation, 
assumes the designation of crus cerebelli. On it the 
cerebellum is developed. It consists essentially of fibres 
from the restiform bodies, re-enforced by others coming 
from the anterior pyramids under the name of arciform 
fibres. These together make their way to the interior 
ganglion of the cerebellum, the corpus dentatum, and 
there they end. But the crus cerebelli contains likewise 
two other great strands : an inferior, constituting the 
commissures of the two cerebellar hemispheres, and 
which, running round the entire prolongations of the 
spinal cord, forms the pons varolii ; a superior, the pro- 
Mis cerebelli ad testes, uniting the cerebellum and 
cerebrum. 

Of the portions of the spinal cord on which the cere- 
brum is to be developed, the sensory end in the optic 
thalamus, the motor in the corpus striatum. The thal- 
amus and striatum of each side maybe regarded as one 
compound ganglion, since, like the columns of the cord, 
they are I by a gray and a white commissure. 

Of the portions on which the cerebellum is to be devel- 
oped, the termination is in the central ganglion of the 
bellum, the corpus dentatnm. 

Bow may the brain be considered as related to the spinal cord? 
IIow does the cerebrum arise ? How does the cerebellum arise? 



236 THE BRAIN. 

At the place of bifurcation of the constituent strands 
of the crus cerebri and crus cerebelli from each other in 
the medulla oblongata, there is intercalated or included 
a ganglion, which, with its apparatus, constitutes the 
olivary body : its fibres make their way upward between 
the two preceding bundles, and, having bifurcated, one 
branch goes to the quadrigemina and the other to the 
optic thalamus, the latter constituting, as has been said, 
a part of the crus cerebri. The seat of power of the 
medulla oblongata is in this ganglion. 

Such being the anatomical construction of the crus 
cerebri, it may be physiologically regarded as a com- 
pound strand^ the anterior portion being motor, the pos- 
terior sensory ; and between these a dark vesicular de- 
posit, the locus niger, continuous between the vesicular 
matter in the spinal cord and that of the thalamus and 
corpus striatum. From the lowest extremity of the 
cord to these great ganglia there is, therefore, an un- 
broken vesicular channel. In its progress onward to 
the corpus striatum, the anterior strand yields roots of 
the spinal accessory, hypoglossal, facial, abducens, the 
small root of the fifth, the trochlearis, and the oculo- 
motor nerves. If there were no other proof of the motor 
character of this strand, the motor property of all these 
nerves would be sufficient to determine it. In like 
manner, the posterior strand yields the pneumogastric, 
the glossopharyngeal, and the sensory root of the fifth ; 
from the sensory functions of these its sensory character 
is established. 

The layer of vesicular matter found upon the cerebral 
convolutions, and which is doubtless the seat of the 
higher intellectual qualities, has therefore no communi- 
cation with the vesicular matter of the spinal axis, by 
contact or continuation, but only through the interven- 
tion of fibres radiating upon it in all directions from the 
thalamus and striatum, or rather through some radiating 
from the great sensory centre, the thalamus, to the pe- 
riphery of the cerebrum, and others converging from 
that periphery to the great motor centre, the striatum. 

What is the olivary body ? What is its function ? What is the 
constitution of the crus cerebri ? What nerves come from its ante- 
rior strand ? What from the posterior ? How is the vesicular mat- 
ter of the cerebral hemispheres arranged ? 



THE BRAIN. 237 



roTTdo 

of an inch, there must be many millions of them in the 
aggregate. The vesicular matter of the hemisphere is 
arranged on the superficies instead of centrally, on ac- 
count of the necessities of their structure and condition 
of activity, for thereby a great surface is obtained; this 
is farther increased by the artifice of convolutions, a ve- 
sicular surface which, counting in that of the cerebellum, 
has been estimated at 670 square inches, and blood can 
be copiously supplied and freely removed. 

But the thalamus and striatum are only two of a chain 
of ganglia beneath the cerebral hemispheres. Anterior- 
ly we find the olfactive ganglia, or bulbs of the olfactory 
nerves, seated upon peduncles, though their character is 
manifest from the gray matter they contain. Behind 
these are the tubercula quadrigemina, to which the op- 
tic nerves run, and therefore their ganglionic centres. 
What answers to the auditory ganglion is lodged at a 
1 distance back, at the fourth ventricle, and the gustatory 
ganglion is in the medulla oblongata. These are the 
ganglia of special sense, and to be regarded as subordi- 
nate to the thalamus, which is their common register. 

All these parts are commissured with one another, and 
with their fellows of the opposite half of the brain. In- 
deed, so likewise are all its parts, the different cerebral 
lobes, the opposite hemispheres, adjacent and distant 
convolutions, the cerebrum with the cerebellum. Hence 
arises a structure of extreme complexity. Among the 
commissural apparatus may be more particularly men- 
tioned the corpus callosum, the fornix, the anterior, the 
posterior, the soft, and the superior longitudinal com- 
missures. 

The ganglia at the base of the brain are regarded by 
Dr. Carpenter as constituting the true sensorium, a doc- 
trine he has established by many weighty arguments, 
and which is doubtless one of the most important thus 
far introduced by physiologists. 

There can be no doubt that the cerebral hemispheres 
constitute the instrument through which the mind exerts 
its influences on the body. Any injury of sufficient se- 

What are the ganglia at the base of the brain? What arc the 
chief commissures of the brain? What constitutes the sensoriom? 

What is the general function of the cerebral hemispheres? 



238 STRUCTURE OF THE CEREBELLUM. 

verity inflicted upon them is at once attended with a to- 
tal loss of intellectual power ; any malformation or lesion 
by disease is attended by a deterioration below the cus- 
tomary mental standard ; any unusual development with 
correspondingly increased powers of intellection; and 
this not only as regards animals of different tribes, or 
individuals at special periods of their lives, but also of 
different men compared with one another. The general 
impression that those who have distinguished themselves 
for mental attainments or intellectual power have been 
marked by the unusual development of their cerebral 
hemispheres is founded in fact. 

We may therefore consider the intellectual principle 
as possessing powers, properties, and faculties of its own ; 
as being acted on by impressions existing in the thala- 
mus, and delivered through the intervening fibrous struc- 
tures to the vesicular material of the convolutions of the 
cerebral hemispheres. In this region they act upon the ( 
intellectual principle and are acted upon by it, the re- 
turning influence, if any, coming down through the con- 
verging tubular structures to the corpus striatum, and 
by its commissural connections sent off to particular 
ganglia, passing along the inferior strand of the crus 
through the mesocephalon to the anterior pyramids, 
and by their decussation to the opposite side of the 
cord. 

Having thus spoken of the sensory ganglia and the 
cerebral hemispheres, it remains to add some remarks re- 
specting the cerebellum. It arises, as has been stated, 
from the triple strand of the crus cerebelli, of which one 
layer of fibres is connected with the corpora quadrigem- 
ina, and through them with the optic thalami ; a second 
with the restiform bodies ; and the third is commissural, 
and passes forward as the pons varolii. 

Like the cerebrum, this organ is vesicular on its sur- 
face, with fissures descending to the interior. Their 
object is apparently the same as that of the convolu- 
tions of the brain, the augmentation of surface. Of 
these fissures, the deep are termed the primary: they 
divide the organ into lobes. Those descending to a less 
depth are termed secondary: the divisions they give 

How does the intellectual principle operate through the brain? 
Describe the position and structure of the cerebellum. 



FUNCTIONS OF THE CEREBELLUM. 239 

rise to arc lobules. The gray vesicular material does 
not, however, descend to the bottom of the primary fis- 
sures, and in this respect they differ from the cerebral 
convolutions. Moreover, from this circumstance, that 
material is not continuous all over the cerebellum, but 
is in divided portions. 

That the cerebellum is one of the sensory ganglia may 
be inferred from the history of its development and its 
anatomical connections. Its median lobe is the first to ap- 
pear, as in fishes, and the hemispheres arise subsequent- 
ly as appendages thereto, as in birds. The size these 
eventually attain gives them a deceptive prominence, 
and hides their subordinate character. Regarding the 
lobe, therefore, as the essential and fundamental portion 
of the structure, the significance of its cerebral connec- 
tion with the thalamus through the processus ad testes 
is too obvious to be overlooked. As by this its sensory 
character is displayed, so the same holds good for the 
hemispheres, their relations with the spinal cord through 
the restiform bodies being also of a sensory nature. It 
seems probable that the superficial vesicular material 
is in anatomical connection with the thalamus, and the 
corpus dentatum or inner ganglia with the posterior or 
sensory columns of the cord. 

The co-ordinating and governing minute muscular 
motions is supposed to be one of the functions of the 
cerebellum. To maintain the standing position motion- 
less, there are, in reality, a great many muscular move- 
ments required, serving to antagonize all the little inci- 
" dents producing a tendency to fall; and if this be so in 
standing, how much more difficult must such antago- 
nizing and compensating actions become in walking, 
running, and such movements. Theoretically, it might 
1 that some Bpecial organ is necessary to 
combine such various actions, and that organ seems to 
be the cerebellum. 

Experimental results appear to strengthen this opin- 
ion. T bellum, on irritation, gives rise to no con- 
vulsive motions, nor to sen If removed by de- 
rive slices, the motions of the animal be- 

What i- ii I jTirt? In what manner is if inppoted to Ik: 

related to i tr motion? Wh:it experiments hare led to that 

opinion ? 



240 FUNCTIONS OF THE CEREBELLUM. 

come irregular, and, finally, it loses all power of walk- 
ing or of maintaining its equilibrium. 

Connected with these results of experimental lesions 
of the cerebellum are the rotations, as they are termed, 
occurring, for example, when one of the crura cerebelli 
is cut, the animal rolling upon its longitudinal axis for 
a long time and with great rapidity. From such facts, 
it has therefore been concluded that the function of the 
cerebellum is neither for sensation nor intellection, nor 
is it the source of voluntary movements, but that it is 
for the government or control of combined muscular 
action. 

It has also been supposed that the cerebellum is for 
the perception of the sensations derived from the mus- 
cles, and enabling the mind to exert a guiding action. 
The facts supporting the preceding view support this 
also, there being, moreover, in this case, an additional 
argument derived from the connection the cerebellum 
has been shown to maintain with the sensory columns 
of the cord, and the pain experienced on irritating the 
restiform columns. It has likewise been pointed out 
that this hypothesis illustrates the connection between 
the cerebellum and the optic ganglia, as if it were for 
the purpose of bringing the organs of sight to the aid 
of this co-ordination of muscular motion. 

A third hypothesis is, that the cerebellum is the or- 
gan of sexual instinct, or of amativeness, as it is termed 
by phrenologists. The evidence of this, when fairly 
examined, is, however, far from affording a full proof: 
indeed, in many instances the facts are in direct opposi- 
tion to the hypothesis. In castrated animals the cere- 
bellum undergoes no diminution. There is no coinci- 
dence between the intensity of that instinct in the dif- 
ferent animal tribes and the degree of development of 
this organ ; and where it has been in a diseased condi- 
tion, there has not been a necessary correspondence be- 
tween the lesion and the loss of the instinct. 

In man, the weight of the brain averages about fifty 
ounces ; in females, about forty-five ; the maximum be- 

What is meant by cerebellar rotations ? Why is it supposed that 
the cerebellum is connected with muscular sensations? What is 
meant by its being the seat of amativeness ? Can that hypothesis be 
maintained ? What is the weight of the brain ? 



ACTION OF THE BRAIN. 241 

ing about sixty-four, and the minimum about twenty. 
The mean specific gravity of the gray matter is stated 
to be, in both sexes, 1.034, but somewhat less early and 
late in life. The specific gravity of the white is 1.041, 
and this varies less with sex and time of life than the 
former. 

The functional activity of the brain depends on the 
copious supply of arterial blood. It is computed that 
one fifth of the whole quantity in the circulation is sent 
to this organ. It is delivered* through the two internal 
carotid and two vertebral arteries. The impetus of the 
current is checked by the sinuous course these vessels 
take, or by their breaking promptly into capillary 
branches. A freedom of anastomosis among them, as 
is well displayed in the circle of Willis, affords abun- 
dant provision for accidental stoppages or restraints. 

Although the brain is inclosed in an unyielding cavi- 
ty, it is subject to the pressure of the air. And since 
the quantity of blood present at any moment in the or- 
gan varies witli the contemporaneous functional activi- 
ty, being greater as that activity is greater, the cerebro- 
spinal fluid also varies in amount. Through this fluid 
an equality of pressure is therefore insured, no matter 
what may be the quantity of blood in the brain. 

The cerebro-spinal fluid, the quantity of which has 
been estimated at two ounces, is readily absorbed and 
as readily reproduced. The act of adjustment between 
it and the blood requiring a certain period for its com- 
pletion, the brain can not instantaneously be brought to 
its maximum action. Thus, as all persons observe, when 
Ave undertake any unusual intellectual duty, there is a 
certain preparatory period to be passed through, as the 
common expression is, " for composing the thoughts." 

-Mire upon the brain, either applied mechanically 
or through accidental effusions, produces at once func- 
tional inactivity, probably by interference with the due 
circulation of the blood ; and, in like manner, any 
marked change in the chemical relations of that fluid 

What i< the specific L r niviry of the brain? What is the relative 
quantity of bl to it? Sow is that supply famished and 

controlled? Does tin- pn asure of the air ad <>n tin- brain? Wh.it 
i- tin; action of the cerebro-spinal fluid? What arc tli<- effects of 
mechanical pressure on the brain? 

i. 



242 PSYCHICAL POWERS. 

exerts on the brain a corresponding effect. Thus, when 
oxygen gas is breathed, or, still better, protoxide of ni- 
trogen, the processes of intellection go on in an exag- 
gerated way, and ideas in rapid succession, and in unu- 
sual forms of combination, flit through the mind ; but, 
as the consequence of this, since the lungs can not re- 
move with the necessary promptness the carbonic acid 
arising, the narcotic effects of that body are soon expe- 
rienced ; and this is also the case in alcoholic intoxica- 
tion, in the advanced stages of which the accumulation 
of carbonic acid in the blood produces the same result. 

That different regions of the brain have independent 
though mutually commissured faculties, is fully estab- 
lished by the phenomena of the nerves of sense, nor can 
there be any doubt that these differences of physiolog- 
ical function are directly dependent on differences of an- 
atomical structure. It is, indeed, to structural differ- 
ences that we should impute the greater or less efficien- 
cy of the whole organ, as much as to differences of its 
weight. Because of a higher elaboration, the' brain of 
one person may be more energetic than that of another, 
even though its weight may be less. It is not to be de- 
nied, however, that there is a connection between men- 
tal power and the quantity of cerebral matter, when in- 
dividuals of the same kind are compared, or that in the 
animal series the psychical powers decline as the cere- 
brum diminishes in size. 

Few topics are more worthy of the attention of the 
physiologist than that of the variable psychical powers 
of man, and yet few have been more overlooked. By 
variable psychical powers I mean those periodicities of 
increase and diminution in our intellectual efficiency, 
noticed not only in diseased, but also in healthy states. 
On the principles we have presented, these find their 
explanation in the temporary physical states of the or- 
gan, such as its condition of repair, its existing facility 
for oxidation, and the constitution of the blood as re- 
spects a proper arterialization. 

The most striking structural characteristic of the nerv- 
ous system is its symmetrical doubleness, the cranial 
and spinal nerves coming forth by pairs to their distri- 

How may it be proved that different regions of the brain have 
different functions ? What is meant by variable psychical powers ? 



DOUBLEXESS OF THE NERVOUS SYSTEM. £43 

bution on the right and left sides of the body. The 
manner of development from the spinal axis laterally 
implies Bach a construction, and, indeed, gives origin to 
two halves so equal and alike, that it has often been said 
each person consists of two separate individuals. Ex- 
amining those organs which, by reason of the elaborate- 
ness of their mechanism and principles of action, enable 
us to determine with satisfactory precision the function 
discharged by each one of the members of the pair, as 
in the case of the eye or the ear, we may come to the 
following conclusions : Each is a distinct organ in itself, 
capable of meeting the requirements of the economy in 
a sufficiently satisfactory manner, and therefore forming 
a distinct whole ; but the pair can likewise act simulta- 
neously, re-enforcing, to a certain degree, each other's 
power, though in this double action there by no means 
arises a double intensity of effect. The closure of one 
ear to a sound does not diminish the loudness by one 
half, nor does the shutting of one eye reduce to one 
half the brightness of a light; but, though there is not 
such a doubling of effect when both eyes or both ears 
are employed, there is a degree of precision in the re- 
sulting indication not to be gained by the use of one of 
these organs alone. In such a double organ, then, the 
result is not so much a heightening of the final impres- 
sion as the giving to it of a greater degree of pre- 
cision. 

Moreover, each organ seems to exert a compensating 
influence over its fellow in any deficiencies or imperfec- 
tions it may possess. Thus it is rare that both eyes are 
of an equal optical goodness, as most individuals will 
find on making a personal examination ; but in vision 
with both eyes, the faults of the more imperfect one are 
merged in the indications of the better, and the same 
might be remarked of the ear; from which it would ap- 
r that this doubleness of organs is rather for the 
purpose of introducing a principle of compensation than 
one of conspiring action, the object intended to be 
gained being a justness of perception rather than an in- 
crease of eff< 

These observations apply to doable organs in their 

How do duublc organa ud ? 



244 INDEPENDENT ACTION OF EACH HEMISPHEKE. 

normal states, or, if not their normal, their habitual 
ones ; but if to the eye, for example, a temporary dis- 
turbance is given, as by pressure, which renders its op- 
tical axis oblique, the fellow organ being permitted to 
retain its usual position, double sight is the result. It is 
true that, in the habitual divergence of strabismus, such 
is not the effect, one of the images disappearing, or per- 
haps the mind, accommodating itself to the habitual 
condition, combines the two into one. These circum- 
stances indicate that each member of a double organ 
can, under conditions of disturbance, exercise an inde- 
pendent and even opposing action to its fellow. 

It has by some been supposed that the mind pays at- 
tention to the impressions of only one of the pair of or- 
gans at a time ; thus, that we see the images furnished 
by only one eye, though we can with very great quick- 
ness direct attention to those furnished by the other, 
and therefore, deceived by the rapidity with which this 
alteration of attention can be accomplished, our belief in 
the synchronous use of both organs is an error. A sim- 
ple experiment illustrates this. If the open hand be 
placed along the nose, so as to divide the right eye from 
the left, and we look upon the surface of a uniformly-il- 
luminated sheet of paper covered with writing, it will be 
found that we can only read with one eye at a time, but 
that the mind can with great rapidity determine which 
eye it will use. In this experiment we have, moreover, 
the means of estimating the relative sensitiveness of the 
two eyes, and other of their optical peculiarities ; thus 
it will be commonly remarked that, though the paper 
be, as we have said, uniformly illuminated, the part of 
it regarded by one eye is brighter than that seen by the 
other, this being due to a difference in their sensibility. 
It will also frequently occur that the two portions of 
the page will present different shades of tint, the one, 
perhaps, being a faint greenish gray, while the other is 
of a yellowish white. 

In this feature of double construction the brain itself 
participates, presenting a right and left half approaching 
one another in form, without being absolutely identical. 
Much, therefore, of what has been said respecting the 

What effect ensues from a temporary disturbance of one of them ? 
How may it be proved that one eye is used at a time ? 



DOUBLE TRAINS OF THOUGHT. 245 

mutual relations of the right and left eye, and the right 
and left ear, must apply to the right and left hemi- 
spheres of the brain. Nor can there be any doubt that 
each hemisphere is a distinct organ, having the power 
of carrying on its functions independently of its fellow; 
that, though each can thus act separately, both can act 
simultaneously; and, judging from the cases that have 
just been presented, it would seem that we are justified 
in inferring that the common action of the two hemi- 
spheres is not for the purpose of a heightening of effect, 
but only for greater precision, and that in the same 
manner as it is a rare thing to find two eyes or two ears 
of equal goodness, so also it is unusual to have two 
hemispheres precisely alike. The defects of the one 
may be compensated by the superiorities of the other, 
and thus a mean result be attained ; and as one eye or 
one ear can, under the proper circumstances, overpower 
its fellow, so likewise can one hemisphere of the brain, 
except in certain cases, somewhat imaginatively de- 
scribed as insubordination of one of the hemispheres, 
when insanity is the result, the healthy half being una- 
ble to control the diseased one ; and for this reason, Ave 
often observe of the insane that they have synchronous- 
ly, or, at all events, in a very rapid alternation, two dis- 
tinct trains of thought, and, consequently, two distinct 
utterances, each of which may, so to speak, be perfectly 
continuous and even sane by itself, but the incongrui- 
ties that arise from the mingling of the two betray the 
condition of such persons. In this case doubleness of 
action is seen in its most exaggerated aspect, but in a 
less degree, it may be remarked, in the thinking opera- 
tions of those whose minds are perfectly sound. Thus 
ry student must have observed, when busily engaged 
in reading, that his mind will wander off to other things, 
though lie may mechanically cast his eyes over page aft- 
er page; and the same may occur in listening to a lec- 
ture or sermon. Bat, though the insane man may in- 
dulge in two synchronous trains of thought, he never 
indulges in three, for the simple reason that he has not 
three hemispheres to do it with, the same remark aj>- 

- each hemisphere of the brain act independently? What is 

meant by insubordination of a liemisjjherc ? How may double 
trains of thought be explained ? 



246 DOUBLE TRAINS OF THOUGHT. 

plying to the sane man in the accidental wanderings of 
his thoughts. 

The overcoming of this insubordination of one of the 
hemispheres may, to a very considerable degree, be ac- 
complished by education, of which one of the chief re- 
sults is that it exercises us in the habit of thinking of 
one thing at a time, of thinking therefore without con- 
fusion, and of arriving at conclusions with precision and 
decision. 

Of the independent and yet complete action of each 
of the cerebral hemispheres we have abundant and in- 
teresting proof. Mental operations can be carried on 
in a profoundly diseased state of one of these organs, as 
multitudes of well-authenticated cases attest — nay, even 
when the lesion has gone so far as to amount to an ab- 
solute and entire disorganization of one of the hemi- 
spheres. Similar evidence is also furnished by interest- 
ing cases in which, by accident, as by gunshot wound, 
destruction of one side has occurred. 

Even in a state of health we have numerous examples 
of this independent action of each hemisphere. While 
engaged in ordinary pursuits implying a continued 
mental occupation, we are occasionally troubled with 
suggestions of a different kind. A strain of music, or 
even a few notes, may be perpetually obtruding, and 
such an occurrence we could scarcely explain save upon 
the principle of the separate action of these organs, the 
one interfering with the other. That precision we have 
remarked as arising from the conjoint use of two eyes 
and two ears is doubtless also attained where the two 
hemispheres are acting in unison. We can, moreover, 
voluntarily permit one to rest while the other continues 
its duty, as we can voluntarily make use of one eye, dis- 
regarding the indications of the other ; but where it is 
necessary to execute a critical comparison or arrive at 
an accurate judgment of things, both hemispheres are 
brought into action, as are both eyes when we intently 
consider an object. 

Among other phenomena, the operation of castle- 
building, as it is designated, illustrates the voluntary 

What effect has education on the use of the hemispheres ? How 
may it be proved that each hemisphere can act perfectly when used 
alone ? Give illustrations of the mixed action of both. 



DOUBLE CONSCIOUSNESS — FEE-EXISTENCE. 247 

maimer in which we permit one hemisphere to act, pre- 
senting fanciful delusions ; the other, as it were, watch- 
ing with satisfaction the operation, and in this respect 
lending itself to it. Xot that for a moment we suppose 
there is any truth in the ideas suggested, and in this the 
phenomenon differs essentially from that of dreaming, 
m which it never occurs to us that the scenes and ac- 
tions are fictitious. 

Still more strikingly do those singular cases, from 
time to time presenting themselves to the physician, of 
double or alternate consciousness, illustrate this isolated 
function of the hemispheres. In some of these, each 
of these portions of the brain has continued its action 
for a period of days, or even weeks, and then, relapsing 
into a quiescent state, has been succeeded by the other, 
thus presenting in some degree an analogy to the facts 
observed in ordinary cases of insanity, so far as the re- 
ciprocating action of the two organs is concerned, but 
differing in the period of duration of their function ; and 
thus, if one of them should have undergone deteriora- 
tion, or have suffered lesion, so that it has been reduced 
to what might be termed an infantile state, the impres- 
sions formerly stored up in it having been for the most 
part lost, or there being an incapacity in it to make use 
of them, the patient will alternately exhibit what has 
been aptly termed child life and mature life. For a few 
days, or perhaps weeks, he will conduct himself in the 
ordinary manner of an adult, reading, reasoning, and 
acting, and then, for a similar period, will pass into a 
condition in which he does not even know his letters, 
and reasons and acts like a child. 

On the same principles an explanation has been given 
of the sentiment of pre-existence. By this term is un- 
derstood that Strange impression, which all persons have 
occasionally observed in the course of their lives, that 
some incident or scene at the moment occurring to 
them, it may be of quite a trivial nature, lias been wit- 
by them once before, ami is in an instant recog- 
nized. Though this opinion that we have seen a pres- 
ent incident onc< sometimes occurs in cases where 
the circumstances are of profound interest to as, the ex- 
Explain castle-building. Bow <l<>es double or alternate conscions- 
What ifl meant by the sentiment of pre-existence? 



248 LOSS OF PERCEPTION OF TIME. 

perience of most persons assures us that it is more fre- 
quently in trivial events. The explanation is, that it 
arises from the almost contemporaneous action of the 
two hemispheres, and that, under the circumstances, we 
have a confusion of memory, and are led to believe that 
there has been, an interval of indefinite duration, when, 
in point of fact, it was an impression in each hemisphere 
closely coincident in point of time. Perhaps here we may 
appropriately recall the well-known fact offered to us in 
dreaming, that there are circumstances under which our 
mental operations are carried forward with the most 
marvelous speed. Thus a sudden sound, a flash of 
lightning, may be incorporated or expanded into a long 
dream, diversified with a various multitude of incidents, 
all appearing to follow one another in an appropriate 
order, and occupying, as we judge, quite a long time, 
yet all necessarily arising in an instantaneous manner, 
for we awake at the moment of the disturbance. Of the 
same kind is that remarkable deception, authentically 
related by those who have recovered from death by 
drowning, that in the last moments of their agony all 
the various events of their past life, even those of a triv- 
ial kind, have come rushing before them with miraculous 
clearness. Mental operations, therefore, both as regards 
old recollections and new suggestions, may take effect 
with wonderful rapidity, and if the sentiment of pre-ex- 
istence is to be explained on the principle of the double 
action of the brain, it must likewise be dependent upon 
' the fact here presented. 

THE CRANIAL NERVES. 

There are twelve pairs of cranial nerves: 1st. The ol- 
factory; 2d. The optic; 3d. The motor oculi; 4th. The 
pathetic; 5th.Thetri-facial; 6th. The abducent; 7th. The 
facial; 8th. The auditory; 9th. The glossopharyngeal ; 
10th. The pneumogastric ; 11th. The spinal accessory; 
12th. The hypoglossal. 

Of these, the first, the second, and the eighth, being 
nerves of special sensation, may be more conveniently 

How may the sentiment of pre-existence be explained ? How is it 
known that the mind may lose all perception of time ? How many 
cranial nerves are there ? Enumerate them. How many are nerves 
of special sense ? 



THE FACIAL NEK YE. 249 

mentioned in connection with the organs of special 
sense — the nose, the eye, the ear. 

The motor-oeuli nerve is wholly motor, as may be 
shown by experiment. When it is irritated the muscles 
it supplies are convulsed, and when it is divided they 
are paralyzed. 

The fourth nerve, or pathetic, is distributed to the 
orbital surface of the superior oblique, or trochlear nius- 

. for which it is the motor nerve. When it is irri- 
tated that muscle is convulsed. 

The fifth nerve lias a construction so closely analogous 
to that of the spinal nerves, that it has been designated 
the spinal nerve of the head. It arises by two roots, 
the anterior of which is the smaller, the posterior having 
a large ganglion, the ganglion of Casser. From the 
ganglion three branches diverge, the ophthalmic, the su- 
perior maxillary, and inferior maxillary. The last re- 
ceives the motor portion of the nerve; the first and sec- 
ond branches are sensory, the third is sensory and motor 
also. 

The sixth nerve is known from its origin, distribution, 
and from experiments made upon it, to be a motor nerve. 

The seventh or facial nerve arises from the upper 
part of the groove between the olivary and restiform 
bodies, and near the pons varolii. With the auditory 
nerve, or portio mollis, it constitutes the seventh nerve 
in the nomenclature of Willis, and derives the name 
portio dura, under which it sometimes passes, from the 
density and closeness of its texture. It supplies all the 
muscles of the face except those of mastication, which 
are supplied by the fifth nerve, those of the palate, the 
09, laxator tympani, and tensor tympani; also 
the muscles of the external ear, and some of those of 
the tongue. The iachd is a centrifugal nerve. If irri- 
tated near its origin, there is no sensation of pain; but 
subsequently it obtains fibres from other source-. 

from the fifth and the pncuinogastrir. .Viler it has 1m.ii 

ted by these, irritation is acutely felt. It is there- 
for a ' neral motor nerve of the 

- eoli nerre? What i< the func- 
nera] construction of the fifth 
nerve. What motions? What is the function of the sixth 

nerve? Describe the facia] n 

i. j 



250 



THE FACIAL NERVE. 



face, influencing the function of respiration through re- 
flex action, but not being connected with the function 
of mastication. Injury of it produces paralysis of the 
parts to which it is distributed, as, for example, the or- 
bicularis palpebrarum, causing inflammation of the eye 
and opacity of the cornea, through inability of that or- 
gan to free itself from dust and spread the lachrymal 
secretion over its surface. In like manner, the sense of 
hearing may be injured through loss of control over the 
muscular structures of the ear, and the acuteness of the 
sense of smell diminished from inability to introduce the 
air in a strong current, or the sense of taste, if the point 
of injury be previous to the giving off of the chorda 
Fig. so. tympani. In paral- 

ysis of the facial 
nerve the muscles 
of the face become 
powerless, and the 
countenance, there- 
fore, distorted. 

Fig. 80: 1, trunk 
of the facial at its 
emergence from the 
aqueduct of Fallo- 
pius ; 2, occipito-au- 
ricular branch; 3, 
auricular of the cer- 
vical plexus ; 4, 
twig of the occipi- 
tal muscle ; 5, twig 
of the posterior au- 

The facial nerve. ricular muscle ; 6, 

twig of the superior auricular; 7, anastomosis of the fa- 
cial with the auricular of the cervical plexus ; 8, branch 
for the stylo-hyoid and posterior belly of the digastric; 
9, temporo-facial anastomosis with the superficial auric- 
ulo-temporal of the fifth pair ; 10, temporal ramifications 
of the facial; 11, frontal twigs; 12, superior palpebral 
twigs; 13, middle palpebral twigs; 14, inferior or mo- 
tor palpebral twigs; 15, suborbital twigs; 16, suborbi- 
tal plexus ; 17, superior buccal; 18, cervico-facial branch ; 




What are the functions of the facial nerve? Describe Fig. 80. 



THE GLOSSO-rilAKYXGEAL NERVE. 251 

19, buccal branches, anastomosing with, 20, buccal nerve 
of fifth pair; 21, mental twigs, forming with, 22, men- 
tal nerve of fifth pair, the mental plexus; 23, cervical 
branches ; 24, transverse cervical branch of the cervical 
plexus ; 25, parotid branches of the superficial auriculo- 
temporal ; 26, parotid branches of the facial ; a, frontal 
muscle ; &, occipital muscle ; C, anterior auricular ; rf, su- 
perior auricular ; 6, posterior auricular ; f, orbicularis 
palpebrarum ; //, zygomaticus major ; Ju buccinator ; ?', 
orbicularis oris ; A*, masseter ; /, parotid gland ; ???, pla- 
tysma; n, stylo-hyoid and posterior belly of digastric; 
o, steruo-cleido-mastoid ; p, trapezius. 

The ninth or glossopharyngeal nerve, examined in 
the usual way, proves to be a centripetal nerve, having 
the power of producing reflex motions through the 
nerves of deglutition, its motor influence being chiefly 
due to its connections with the pneumogastric and ac- 
cessory. Though thus a sensory nerve, it is doubtful 
whether it be the only nerve of taste, or whether that 
function is not likewise participated in by the lingual 
branch of the fifth pair. It is certain that section of the 
lingual does not destroy the sense of taste, and also that 
those parts of the tongue to which the glossopharyn- 
geal is distributed present that sense in the most marked 
manner. The inference usually drawn is that this nerve 
and the lingual are both tactile and gustative, and this 
renders appropriate its description in this place rather 
than among the nerves of special sense. 

The tenth, par vagum, or pneumogastric nerve, arises 
by >ix or right filaments from the groove between the 
olivary and res ti form bodies below the glosso-pharyn- 
1, and, like it, may be traced to the vesicular mate- 
rial of the floor of the fourth ventricle. It first presents 
a small ganglion, and soon after a Becond, nearly an inch 
in length, called the plexus gangliformis. The nerve 
then descends the neck in the sheath of the carotid \ 

9, and in liffers on the right and left sides 

. On the right side it pass< - between the 
•lavian artery and vein, descending toward the Stom- 
ach lar plexus on tl nor portion of the 

i arly parat 

Dfl <>f the ninth ik: tenth 

nerve originate? How u it distribut 



252 THE PNETJMOGASTEIC NERVE. 

lei with the left subclavian, and passes to the stomach 
and solar plexus along the anterior portion of the oesoph- 
agus. 

The chief branches of the pneumogastric are the au- 
ricular, the pharyngeal, the superior laryngeal, the car- 
diac, the inferior laryngeal or recurrent, the anterior 
pulmonary, the posterior pulmonary, the oesophageal, 
and the gastric. 

The pneumogastric presents several plexuses in its 
course, and, even when distributed on the stomach, ex- 
hibits flat, membraniform ganglia. It supplies three 
great classes of organs: 1st. The digestive, as the pha- 
rynx, oesophagus, stomach, liver; 2d. Respiratory, as 
the larynx, trachea, lungs ; 3d. Circulatory, as the heart 
and great vessels. It associates itself intimately with 
the sympathetic, and aids it in forming several great 
plexuses. 

At its root the pneumogastric is sensory, but in its 
trunk it possesses a double function, arising from its in- 
termingling with other nerves, as the spinal accessory 
and sympathetic. Though the trunk, if irritated, gives 
rise to pain, we are not, under ordinary circumstances, 
conscious of indications, as, for example, in the act of 
breathing, in which we do not perceive the necessity of 
respiration, except the access of the air be too long de- 
layed. The pharyngeal branch is the chief motor nerve 
of the pharynx and palate. The superior laryngeal is 
the sensory nerve of the larynx, the inferior laryngeal 
being the motor. Considered along with, the spinal ac- 
cessory, the pneumogastric presents an analogy to a spi- 
nal nerve ; the accessory constituting the anterior or 
motor root, and the pneumogastric, with its ganglion, 
the sensory root. 

The pneumogastric nerve was formerly regarded as 
taking an influential part in the action of the stomach 
during digestion. The precise nature of its agency in 
this respect has been already alluded to. In addition, 
it may be remarked that probably through this nerve is 
the sensation of hunger conveyed to the mind. 

Fig, 81: 1, 1, 1, the left pneumogastric nerve; 2, an- 
astomosis of it with the hypoglossal ; 3, anastomosis of 

What are the functions of the tenth nerve? Describe Fig 81. 






THE FXEUMOGASTRIC XKKVK. 
Fin. 81 



253 




The left pneumogfcstric nerve. 

plexiform ganglion with internal branch of the Bpinal; 
4, pharyngeal, passing in front of the internal carotid 
artery; 5, superior laryngeal, behind the internal caro- 
tid artery; 6, externa] laryngeal; 7, laryngeal plexus, 
formed by external laryngeal and great sympathetic; 8, 



254 SPINAL ACCESSORY AND HYPOGLOSSAL NERVES. 

superior cardiac; 9, middle cardiac ; 10, 10, inferior la- 
ryngeal, or recurrent, forming a curve round the arch 
of the aorta ; 11, pulmonary ganglion ; 12, its anastomo- 
sis with the great sympathetic; 13, posterior pulmona- 
ry plexus; 14, oesophageal plexus; 15, curves formed 
around the oesophagus by the right and left pneumogas- 
trics ; 16, oesophageal strand traversing the diaphragm ; 
17, plexus formed by the strand upon the anterior face 
of the cardiac end; 18, branches for the great end of 
the stomach; 19, branches for the small curvature; 20, 
branches for the anterior face of the stomach; 21, he- 
patic branches commingling with the hepatic plexus of 
the great sympathetic, and ramifying in the substance 
of the liver; 22, glosso - pharyngeal ; 23, its lingual 
branch ; 24, pharyngeal branch ; 25, branch for the stylo- 
pharyngeal muscle ; 26, spinal ; 27, internal branch, aid- 
ing to form the pharyngeal nerve ; 28, external branch ; 
29, twig of external branch anastomosing with the third 
cervical ; 30, anastomosis with trapezian branch of the 
fourth cervical ; 31, cervical portion of the great sympa- 
thetic ; 32, 32, thoracic portion ; a, thyroid body ; 5, tra- 
chea ; c, left lung, drawn to the right ; c?, liver, raised ; 
6, oesophagus ; f, great end of the stomach, drawn to 
the left ; g, arch of the aorta ; the carotid, and subcla- 
vian arteries, cut. 

The eleventh, or spinal accessory, is a motor nerve, as 
appears from the usual evidence of irritation, and also 
from its origin and distribution. Its action is not essen- 
tial in ordinary or involuntary respiration. In voluntary 
respiration it is brought into play. 

The twelfth, or hypoglossal, is the motor nerve of the 
tongue, irritation of it giving rise to movements through- 
out that organ, the lingual branch of the fifth being the 
sensory. The hypoglossal causes the muscles of the neck 
to aid in the movements necessary for articulate speech. 

OF THE GREAT SYMPATHETIC NERVE. 

Under the designations of sympathetic, visceral, tri- 
splanchnic, ganglionic, intercostal, or nerve of organic 
life, passes a series of reddish or gray ganglia, intercon- 

What are the functions of the eleventh nerve ? What are the 
functions of the twelfth nerve? Under what names does the sym- 
pathetic pass ? 



ORIGIN OF THE SYMPATHETIC NERVE. 255 

nected by nervous strands, extending along each side of 
the vertebral column, from the head to the coccyx, com- 
municating with all other nerves of the body, and dis- 
tributing branches to the internal viscera, or organs of 
involuntary function. These ganglia are less numerous 
than the vertebrae ; the chain on each side communicates 
with its colleague through plexuses, and the ganglion 
impar is the common uniting point on the coccyx be- 
low. By some it is supposed that the ganglion of Ribes, 
and by others that the pituitary body has the same func- 
tion in the cranium above. What are here spoken of as 
nervous strands are perhaps more correctly prolonga- 
tions of the ganglia themselves. 

The origin of the sympathetic has been long a subject 
of dispute, some supposing that it is a special system, of 
which the ganglia are so many independent centres, es- 
tablishing incidental communications with the cerebro- 
spinal ; others, that its origin is in the internal viscera, 
and its termination in the cerebro-spinal system, this 
opinion being supported by the alleged facts that the 
sympathetic, in its development, appears before the oth- 
er parts of the nervous system, and simultaneously with 
the splanchnic organs, and that it has been found in 
monsters without a brain or spinal cord ; others, again, 
suppose that it originates from the roots of the cerebro- 
spinal system, and terminates in the interior organs. 
Regarding it in this light, some have imputed its origin 
to all the spinal, and fifth and sixth cranial conjointly; 
others have limited it to the two latter. 

The pneumogastric nerve aids it in forming three of 
its plexuses, the pharyngeal, cardiac, and solar. In cer- 
tain respects the pneumogastric and sympathetic seem 
to exhibit a reciprocal development, in some of the low- 
er animals the former predominating over, and supply- 
ing the place of the latter; and this replacement, it is 
said, goes on in the descending series until, in the ceph- 
alopodous mollusks, tl^e sympathetic has disappeared, 
and the pneumogastric takes its place. 

Fig. 82 (page 250) illustrates the relation of the sym- 
pathetic and spinal nerves: c c, anterior fissure of the 
spinal cord ; a, anterior root of a dorsal spinal nerve ; p, 

What is its position? How docs it originate? What arc its re- 
lations to the pneumogastric ? Describe Fuj. 82. 



256 RELATION OF THE SYMPATHETIC AND SPINAL. 



Fig. 82. 



posterior root, with 
its ganglion; a\ an- 
terior branch ; p\ 



posterior branch ; 
s, sympathetic ; 6, 
its double junction 
with the anterior 
branch of the spi- 
nal nerve by a white 
and a gray filament. 
The sympathetic 
chain therefore es- 
tablishes connec- 
tions with the cer- 
ebrospinal system. 
Each spinal nerve 
is brought into rela- 
tion with it through 
two strands, a tubu- 
lar or white, and a 
gelatinous or gray. 
The tubular or 
white strand may 
be regarded as act- 
ually arising from 

Relation of the sympathetic and spinal. the Spinal COl'd, and 

consisting of motor and sensory filaments. It makes its 
way to the ganglion of the sympathetic, passes over and 
through it, its fibres conjoining themselves with gray 
ones, which they have gathered in the ganglion. The 
gray or gelatinous root is to be viewed as having its ori- 
gin in the ganglion of the sympathetic, and sending its 
fibres chiefly to the ganglion on the posterior root of 
the spinal nerve, but few of them doubtfully communi- 
cating with the anterior root. The fibres which seem to 
enter the cord are probably for the supply of blood-ves- 
sels. Each of these sympathetic ganglia is therefore a 
nervous centre, sending forth strands in three directions : 
1st. To join the spinal fibres in their distribution ; 2d. 
To the spinal cord itself, or chiefly to the ganglia on the 
posterior roots of its nerves; 3d. To the next sympa- 

How is the sympathetic connected with the spinal system? What 
nerve supplies originate from the sympathetic ganglia ? 




THE GEE AT SYMPATHETIC. 25 7 

tbetic ganglion above. In the various plexuses of the 
sympathetic, vesicles are found, from which gray fibres 
seem to originate. The branches supplying the viscera 
constantly form plexuses ; the arteries are surrounded 
with such a net-work. The splanchnic ganglia, w r ith 
their interconnecting strands, and supplies from the cere- 
brospinal, give rise to four great plexuses: the pharyn- 
geal, the cardiac, the solar, and the hypogastric. The 
first and last of these are in symmetrical pairs ; the oth- 
er two are single, and placed on the median line. 

From its construction the sympathetic can not be re- 
garded as an isolated or self-acting system, since all its 
branches contain fibres derived from the cerebro-spinal. 
In function it must therefore be adjuvant to that system, 
and it must be admitted that the motor and sensory 
qualities of the included spinal fibres, according as they 
have been derived from the anterior or posterior col- 
umns of the cord, are continued in their association 
with the*sympathetic. Hence, in so far as being a com- 
pound nerve, it possesses both those functions, and this 
conclusion is corroborated by such facts as those of the 
distribution of the sympathetic both to muscular por- 
tions, as to the heart, and also to sensitive ones ; by the 
circumstance that the intestinal canal from the stomach 
to the end of the colon receives its nervous supply from 
this source alone. Experiments on the sympathetic 
ganglia establish a similar conclusion, irritation of the 
celiac ganglion, for instance, giving rise to increased 
peristaltic motions, and pathological observations fur- 
nishing like evidence as regards the sensory function. 
Compared with other nerve trunks, the sympathetic is 
much less active in these respects, a high irritation of 
the parts supplied by it often being required to cause 
pain, and, in like manner, its motor fibres are little un- 
der the influence of the will. 

The sympathetic transmits sensations so tardily that 
it 1. d that one office of its ganglia is for 

the purpose of cutting Ml' such impressions ; and, in like 
manner, when motor fibres of the cerebrospinal system 
- through its ganglia, their conducting power appears 
to be impaired. There does nol seem to be any decisive 

What are the four chief sympathetic plexuses? What are 
of the chief functions of the sympathetic? 



258 THE GEE AT SYMPATHETIC. 

proof that any of the fibres of the sympathetic, proper- 
ly speaking, are motor or sensory, or that its ganglia 
produce reflex action, the agency it exerts in these re- 
spects on the muscular structure of the heart, blood- 
vessels, digestive or urinary organs, being due to the 
associated cerebro-spinal fibres. 

In this manner, by its distribution to the arteries, the 
sympathetic, as a compound nerve, exerts a power over 
the passage of the blood through them by influencing 
their contractility, and thereby their diameter. In vir- 
tue of this, it therefore affects the rapidity of secretion, 
and alsO regulates the rate of nutrition. The entire di- 
gestive tract, with its dependencies, is thus brought un- 
der its influence, the salivary glands, pharynx, oesoph- 
agus, stomach, intestine, nasal, bronchial, and pulmonary 
surfaces, etc. 

The view of the function of ganglia presented on 
preceding pages is strongly supported by the mechan- 
ism and phenomena of the sympathetic nerve. * Its gan- 
glia permit the influence passing along the nervous 
cords to escape therefrom into new channels, and also 
retain and store up nervous power. They become, 
therefore, magazines of force, and are hence capable of 
sustaining rhythmic movements. Even after organs 
have been exsected, they will still exhibit, under the in- 
fluence of these ganglia, their accustomed motion, as is 
the case with the heart, which, in some of the cold- 
blooded animals, will continue its contractions for many 
hours after it has been cut out of the body. 

I therefore regard the sympathetic system as having 
for one of its main functions the equalization or balanc- 
ing of the nervous force, storing up all transient excess- 
es of it, and furnishing all transient deficiencies. As in 
a mechanical contrivance, in which the prime mover 
works in an irregular way, the fly-wheel harmonizes all 
such variations, storing up or supplying power as the 
circumstances may require, so does this complicated ap- 
paratus act in the mechanism of innervation. And it is 
worthy of remark, that some such afrangement would 
seem to be necessary, since the organs of digestion, to 

How does it act on the arteries ? What are its relations to the di- 
gestive tract ? What is the physical function of its ganglia ? Give 
a summary of the functions of the sympathetic. 



THE GREAT SYMPATHETIC. 259 

which the sympathetic is so largely directed, are peri- 
odically in activity and periodically quiescent. 

Fig. Sd (page 2(30) : 1, globe of the eye, dissected so 
as to show the ciliary nerves; 2, branch of the inferior 
oblique and the motor root of the ophthalmic ganglion; 
3, 3, 3, the three branches of the trifacial, in connection 
with most of the cranial ganglia, that is, with, 4, oph- 
thalmic ganglion, 5, sphenopalatine, 6, otic, 7, submaxil- 
lary, and, S, sublingual; 9, external motor oculi ; 10, fa- 
cial and its anastomoses with the spheno-palatine and 
otic ganglia; 11, glossopharyngeal ; 12, 12, right pneu- 
mogastric; 13, left pneumogastric ; 14, spinal; 15, hypo- 
glossal ; 16, 16, cervical plexus; 1 7, brachial plexus ; 18, 
18, intercostal nerves ; 19, 19, lumbar plexus ; 20, sacral 
plexus; 21, superior cervical ganglion, furnishing two 
carotid branches, forming the carotid plexus around the 
artery of that name, and from which arise the anastomo- 
ses with, 22, nerve of Jacobson, 23, carotid branch of 
vidian nerve, 24, external motor oculi, 25, ophthalmic 
ganglion; 26, twig for the pituitary gland; 27, anasto- 
mosis of superior cervical ganglion with the first cervical 
pairs; 28, carotid and pharyngeal branches ; 29, pharyn- 
geal and intercarotid plexus ; 30, laryngeal branch, anas- 
tomosed with the external laryngeal of the pneumogas- 
tric ; 31, superior cardiac nerve; 32, strands of junction 
of the superior cervical ganglion with, 33, middle cervical 
ganglion : among the internal branches of the latter are, 
34, the anastomotic with, 35, the recurrent nerve, 36, 
middle cardiac nerve; 37, strand of junction of middle 
cervical ganglion with, 38, inferior cervical ganglion; 
40, twigs furnished by inferior cervical ganglion around 
the subclavian and vertebral arteries; 41, anastomotic 
branch with the first intercostal nerve ; 42, cardiac plex- 
us and ganglion ; 43, 44, secondary plexuses of right and 
left coronary arteries ; from 45 to 46, thoracic gangli- 
onar}- chain ; 47, the great splanchnic traversing the di- 
aphragm, and going to, 48, semilunar ganglion ; 49, little 
splanchnic; 50, solar plexus, receiving, 51, anastomosis 
of pneumogastric, 52, phrenic nerve; 53, gastric coro- 
nary; 54, hepatic; 55, splenic; 50, superior mesenteric, 
enveloping the arteries of those names ; 57, renal plexus; 
from 58 to 58, lumbar 'ganglionic chain ; 59, lunibo-nor- 
Describe Fvj. 83. 



260 



THE GREAT SYMPATHETIC. 

Fig. 83. 




The great sympathetic nerve. 



OF THE SENSES. 261 

tic plexus, presenting two enlargements, one, 60, above, 
the other, 61, below the bifurcation of the aorta; 62, 
spermatic plexus; 63, inferior mesenteric; 64, hypogas- 
tric plexus ; 65 to 65, sacral ganglionic chain ; 66, term- 
inal coccygeal ganglion ; A, heart, slightly turned aside 
to show the cardiac plexus ; B, arch of the aorta, also 
drawn aside by hook; C, innominata; D, subclavian, 
cut, to show inferior cervical ganglion ; E, inferior thy- 
roid ; F, portion of external carotid ; G, internal caro- 
tid ; H, thoracic aorta ; I, abdominal aorta ; J, primitive 
iliac; K, intercostals ; L, pulmonary artery, of which the 
right branch is cut ; M, superior vena cava, cut at its 
origin ; 31, vena cava inferior ; O, pulmonary veins ; a, 
lachrymal gland ; b, sublingual gland ; c, submaxillary 
gland ; d, thyroid body ; e, trachea; /*, oesophagus, going 
to, g, the stomach ; h, several intestinal loops with supe- 
rior mesenteric plexus ; i, transverse colon ; j, sigmoid 
flexure ; k, rectum ; I, bladder ; m, ureter ; n, prostate ; 
o, vesicula seminalis ; p, vas deferens ; q, spermatic cord ; 
r, r, diaphragm. 



CHAPTER XV. 

OF HEARING. 

The Senses : Five Organs of Sense. 

Of Hearing. — General Structure of the Organ of Hear- 
ing. — Physical Peculiarities of Sounds, Intensity, 
Time of Vibration, and Quality. — The Tympanum, 
Cochlea, and Semicircular Canals are for the Appre- 
ciation of these peculiarities. 

OF THE SEXSES. 

The animal being in its highest development, re- 
quires means for the perception of time, space, force, and 
quality. This is accomplished by what are termed the 
organs of sense. They are five in number : 1st. The or- 
gan of hearing ; 2d. That of seeing ; 3d. That of touch- 
ing ; 4th. That of smelling ; 5th. That of tasting. The 
ear is the organ of time ; the eye that of space ; the tac- 
tile apparatus is for the perception of force ; and the 

To what functions arc the organs ot* sense respectively devoted ? 



262 



OF HEARING. 



mechanisms for smelling and tasting conjointly determ- 
ine the chemical qualities of bodies ; that of smelling 
addressing itself to substances in the vaporous and gas- 
eous state, and that of tasting to such as are liquid or 
dissolved in water. 



OF HEARING. 

The organ of hearing is composed of three parts, the 
external ear, the tympanic cavity or tympanum, and the 
labyrinth. 

Of these three portions of the ear, the external canal 
is, of course, full of air, as is also the tympanic cavity or 
drum ; but the labyrinth is filled with a liquid, and in 
this the terminal filaments of the auditory nerve are 
placed. 

The essential part of the mechanism of hearing is the 
auditory nerve, which arises from the anterior wall of the 
fourth ventricle, and then, joining the facial, passes for- 
ward upon the crus cerebelli ; reaching the meatus, it 
divides into two portions, the cochlear and vestibular 



Fig. 84 



nerves: these subdi- 
vide again, and are dis- 
tributed to the vesti- 
bule and cochlea re- 
spectively. 

Fig. 84 : a a, pavilion 
and external auditory 
canal, or external ear ; 
5, tympanic cavity, 
containing the bones; 
c, hammer audits three 
muscles, viz., c?, inter- 
nal muscle, lodged in 

External, middle, and internal ear. t ^ e thickness of the Su- 

perior wall of Eustachian tube, and bending at a right 
angle to be inserted in superior part of handle of ham- 
mer ; 6, anterior muscle of hammer ; y, external muscle 
of hammer ; g, interior half of membrana tympani, hold- 
ing the handle of the hammer ; A, tube of Eustachius ; 
% internal ear or labyrinth. 

Of how many parts is the organ of hearing composed ? What 
media are in the three portions of the ear ? What is the origin and 
distribution of the auditory nerve ? Describe Fig. 84. 




OF THE EAR. 263 

The explanation usually given of the functions of these 
various parts is as follows : The waves of sound, moving 
through the atmosphere, pass down the exterior canal 
and strike upon the membrane of the drum, which is 
thrown into vibration thereby. The little bones form- 
ing a chain from this membrane to the oval one at the 
back of the drum participate in this movement, and, in- 
deed, serve to convey it, without much loss, across the 
cavity. Under the impulses thus communicated to it 
the oval membrane commences to vibrate, and in those 
movements the water in the labyrinth joins ; and so the 
filaments of the auditory nerve become affected, and the 
sensation of sound is transmitted to the brain. • It is sup- 
posed that the three semicircular canals, which are set 
at right angles to one another, as it were, occupying the 
three adjoining faces of a cube, are for the purpose of 
determining in what direction the sound is coming — 
whether upward, downward, or laterally. Moreover, it 
is believed that the little muscles which operate on the 
membrane of the drum have the duty of tightening or 
slackening it so as to receive the sounding waves in the 
most available way. 

It is not necessary to enter on a lengthy criticism of 
this explanation. Physiologists have long regretted that 
it assigns no use for many of the most complicated and 
delicate arrangements connected with the ear, offers no 
explanation of the manner in which that intricate organ 
is enabled to present to the mind the various relations 
of sound, and is inconsistent with many of the facts of 
comparative anatomy. 

What are the physical peculiarities existing in the 
waves of sound? They are these three, 1st. The inten- 
sity, that is, loudness or feebleness of the sound ; 2d. Its 
note or pitch ; 3d. Its quality ; for two sounds of the 
same intensity and note may differ characteristically. 
The sound of the violin differs from that of the flute, 
and this, again, from that of the human voice. Our or- 
gan of audition is so constructed that it is affected by 
each of these peculiarities, and transmits them to the 
mind. All mathematicians who have written on the sub- 

What is the common hypothesis of audition ? What arc some of 
the defects of this hypothesis? What arc the three physical peculi- 
arities of sound ? 



264 STRUCTURE OF THE DRUM. 

ject of sound agree in setting forth the three peculiari- 
ties that have been mentioned, intensity, note, quality, as 
the grand features of waves of sound, and this upon a 
mere abstract discussion of acoustics. Now these three 
essential, abstract, or theoretical peculiarities of sound- 
waves are the very three which the organ of hearing 
seizes upon. Premising the remark that mathematicians 
have abundantly proved that the intensity of sounds de- 
pends upon the amplitude of excursion of the vibrating 
particles, and the pitch or note upon wave length, I shall 
now proceed to offer some arguments in proof of the 
proposition that the triple function of the ear is dis- 
charged in the following way : 1st. That the drum is for 
the measurement of the intensity ; 2d. The cochlea for 
the recognition of wave length ; 3d. The semicircular 
canals for the appreciation of quality. 

1st. On the measurement of the intensity of sound, 
structure of the tympanic cavity or drum, and its func- 
tions. 

The tympanic cavity, or drum of the ear, is an air cav- 
ity of a cylindroid and flattened shape, in the petrous 
portion of the temporal bone. Outwardly it is bounded 
by the membrana tympani, and on other sides by the pe- 
trous bone : it is crossed by a chain of bones, three in 
number, and named the malleus or hammer-bone, the in- 
cus or anvil, and the stapes or stirrup. The Eustachian 
tube affords a channel of communication from the inte- 
rior of the drum to the pharynx. Moreover, there is a 
communication with the mastoid cells, but the Eustachian 
tube is the only outlet to the atmosphere. The whole 
cavity of the tympanum is lined with mucous membrane 
and ciliated epithelium, which is also reflected over the 
bony chain. Upon the inner wall of the tympanum are 
two chief apertures, the fenestra ovalis and the fenestra 
rotunda, eaeh closed by membrane. The chain of bones 
is attached at one end by the handle of the malleus to the 
membrana tympani, at the other by the foot of the stir- 
rup to the membrane of the fenestra ovalis. 

It is to be remarked that the membrana tympani is 
placed obliquely at the bottom of the external canal. 

What is the function of the drum of the ear ? What is that of the 
cochlea? What is that of the semicircular canals? Describe the 
structure of the drum ? 



THE TYMPANUM. 2G5 

In a hollow bony cone, rising upon the interior wall of 
the tympanum, and called the pyramid, the stapedius 
muscle is placed. Through a little aperture at the apex 
of the pyramid its tendon goes out, and is inserted in the 
neck of the stapes. Its action seems to be to make press- 
ure on the membrane of the fenestra ovalis, but as it does 
this, it tilts the stapes into an oblique position. A sec- 
ond muscle, the tensor tympani, is attached in front to 
the under surface of the petrous bone, and is inserted 
in the short process of the malleus ; when it contracts it 
makes tension upon the membrana tympani, drawing it 
more tightly inward. It is to be especially remarked 
of both^hese muscles that they are voluntary; that is, 
of the striated variety. 

The tympanum is for determining the first property 
of sounding waves, that is, their intensity. 

It has been proved that when the tension of the 
membrana tympani is increased, sonorous undulations 
pass with less readiness through it. Indeed, this may 
be verified by personal experiment, as when, by a strong 
effort of expiration or inspiration, the mouth and nostrils 
being closed, we compress air into the tympanic cavity 
or withdraw it therefrom through the Eustachian tube, 
and thereby stretch the membrana tympani outwardly 
or inwardly, the hearing at once becomes indistinct, and 
sounds are enfeebled. 

Under natural circumstances, a stretching of the mem- 
brane inwardly is accomplished by the contraction of the 
tensor tvmpani muscle, the stapedius holding tight con- 
temporaneously on the loop of the stirrup, and prevent- 
ing disturbance of position of the bony chain at that end, 
and hindering any outward bulging of the membrane 
of the fenestra ovalis. When, therefore, the soniferous 
waves impinge upon the membrana tympani, they tend 
to throw it into vibration ; the tensor tympani contracts 
to such an extent as to bring the membrane to a stand- 
ard of tension, and, since this muscle is of the voluntary 
kind, the mind judges of the degree of force required to 
produce that result just as, when we lift from the ground 
lies of different weights, we judge witli a certain 

What h the action of the stapedius and tensor tympani muscles? 
What is the effect of changing the tension of the membrane of the 

drum ? Describe the action of its muscles, 

M 



266 THE EUSTACHIAN TUBE. 

precision of the degree of force necessary to be put 
forth. The condition of contraction of the tensor tym- 
pani therefore enables the mind to measure the intensi- 
ty of the sounding waves. 

But this muscular contraction is strictly a reflex act, 
and is therefore preceded, as all such acts are, by an im- 
pression. That impression is made, as we shall present- 
ly find, primarily on the auditory nerve. But, since these 
reflected acts are not sensory, the mind has no knowl- 
edge of the effect impressed in this respect upon the 
auditory nerve, and only becomes sensible of it in an in- 
direct way, through the contractions ensuing in the ten- 
sor tympani muscle. 

In this view of the case, the use of the Eustachian tube 
becomes obvious ; it is to form a ready passage for the 
air inwardly or outwardly, so that no condensation or 
rarefaction shall occur within the tympanic cavity ; for 
such rarefactions and condensations would disturb the 
action of the contracting muscle, and make it yield a 
false estimate. Besides this, the Eustachian tube, as has 
long been known, affords an outlet for mucus. 

The function of the ossicles is therefore rather for the 
purpose of tension than of conduction, though it is not 
denied that sounds may pass readily along them. They 
are to be regarded as aiding in the perfection of auditory 
perceptions, but yet not as being absolutely essential to 
the appreciation of sounds, or even of their finer modifi- 
cations. Whatever affects the facility of vibration of the 
membrana tympani, such as its thickening, or stiffening, 
or unusual dryness, will render the hearing dull, but the 
membrane itself may be perforated, or even undergo ex- 
tensive lesions, without any apparently corresponding ef- 
fect. But if the stapes be injured or be removed, deaf- 
ness is at once the result. 

There is nothing remarkable in the precision with 
which the contractions of the two muscles acting on the 
membrane of the drum are made. The same precision 
is illustrated in the case of the muscles of the vocal cords. 
The state of these may be determined to the 17 ^ 00 part 
of an inch. 

How is it that the mind perceives their state ? What is the use 
of the Eustachian tube ? What is the function of the ossicles ? With 
what precision may the contractions of the muscles of the vocal cords 
be estimated ? 



STRUCTURE OF THE COCHLEA. 267 

It might perhaps be inquired, Why should not the 
function of determining the intensity^of sounds, as well 
as their wave length, be imputed directly to the auditory 
nerve ? It is with the ear as with the eye, the mechan- 
ism for determining wave length can only act with uni- 
formity when the agent to be measured is reduced to a 
standard intensity. A bright light tailing upon the eye 
brings on a contraction of the pupil. And so with the 
ear. A partial deafening must be established to adjust 
the intensity of sound, that the auditory nerve may act 
under standard circumstances. The primary impression 
therefore made upon that nerve by the loudness of sounds 
is, so to speak, consumed by being converted as a reflex 
act into motion, because there is a necessity that the ten- 
sor and stapedius should move, and reflex acts do not 
affect the mind, but it instantly perceives the condition 
of contraction of those muscles, and so estimates the in- 
tensity of the sound. 

2d. On the measurement of wave length, or time of 
vibration of sounds. Structure of the cochlea and its 
functions. 

The cochlea has been described as resembling a snail's 
shell in appearance. It is a conical tube, wound spiral- 
ly, and making two and a half turns. The interior of 
this conical and spirally-winding tube is divided through- 
out its length into two portions by means of a transverse 
partition, which, following the spiral winding of the 
tube, has had the name of lamina spiralis bestowed on 
it. The two partitions produced by the intervention of 
this lamina are called scala vestibuli and scala tympani. 
At the top or point of the helix the two scalae commu- 
nicate through a little hole, from the cessation of the la- 
mina spiralis. To this opening or deficiency the name 
of helicotrema is given. Considering the two scake as 
separate tubes, their mouths open differently; the scala 

rtibuli opens into the vestibule of the labyrinth, and 
we may therefore regard the membrane of the fenestra 
ovalis B8 being virtually its boundary or closure, but the 
month of the scala tympani is against the fenestra rotun- 
da, and is dosed by the membrane of that aperture. As 
their names therefore indicate, the scala vestibuli opens 

What an : re between the pupil of the eye and the drum 

of the ear ? Describe the construction of the cochlea. 



:r% 




268 THE SPIRAL LAMINA. 

into the vestibule, and the scala tynapani into the tym- 
panum. 

Passing directly through the body of the cochlea, and 
being, as it were, the core upon which that structure is 
built, is a bony cone, called the modiolus. Indeed, the 
bony part of the transverse plate separating the tube of 
the cochlea into its two scalse might be regarded as a 
spiral process of the modiolus. Through the modiolus 
and its spiral process, or lamina spiralis, the auditory 
nerve gains access, through suitable channels, to the in- 
terior of the scalse. 

Fig. 85. Fig. 85, interior of the 

cochlea, rendered. visible by 
the removal of half of the 
outer wall : a a, lamina spi- 
ralis, turning by its inner 
edge, 5, around the axis of 
the cochlea; c, infundibu- 
lum ; c7, aperture of commu- 
interior of the cochlea. nication between two scalae; 

e e, section of the outer wall ; fff, inferior or tympanic 
scala ; g g g, superior or vestibular scala. 

It is necessary to understand the structure of the la- 
mina spiralis more particularly. As we have said, it di- 
vides the helical tube into the two scalse by extending 
transversely across it. Its bony portion does not, how- 
ever, extend more than about one third of the distance, 
the rest of it being made up in part of a delicate mem- 
branous portion, and completed by a muscular structure ; 
so that, if we consider the lamina spiralis at any point, 
the region of it near the modiolus is bone, the interme- 
diate portion membranous, and the residual muscular. 
Or, considering the lamina spiralis in the aggregate, we 
might say that it consists of a helix of bone, membrane, 
and muscle. To the muscle the name of the cochlearis 
is given. Its obvious function is to tighten the mem- 
branous region. Moreover, considered thus in the ag- 
gregate, the lamina spiralis is a triangular plate wound 
round upon a central conical core, and, therefore, broad- 
est at the base of the cochlea, and gradually tapering 
off toward the apex. It is to be understood that the 

How is the auditory nerve introduced ? Describe Fig. 85. What 
is the construction of the spiral lamina? 



FUNCTION OF THE COCHLEA. 



269 



cochlea, like all other portions of the labyrinth, is filled 
with water. 

Upon the spiral lamina, issuing forth through its bony 
portion, are placed the ultimate filaments of the auditory 
nerve. These, having cast oft' their white substance, come 
into relation with elongated vesicles, and are thus distrib- 
uted upon the membranous portion, the membrane be- 
ing kept uniformly tense by the action of the cochlearis 
muscle. 

Fig. 86, section of the cochlea, magnified six diame- 
ters, to show the distribution of the cochlear branch of 
the auditory nerve. 

Fig. 86. 




Distribution of cochlear nerve. 

The principles of acoustics would lead us to infer that 
sounds entering the cochlea throw into vibration its spi- 
ral lamina, an inference supported by anatomical consid- 
erations in regard to the position and function of the 
cochlearis muscle in keeping the membranous portion 
of the lamina at a due degree of tension. We should 
also infer that each external sound does not throw the 
lamina into vibration throughout its whole length, but 
only on a special and corresponding point, and thereby 
affects solely the filament of the auditory nerve in con- 
nection with that point; that sounds which are low will 
act upon the broader portions of the membrane, near 
the mouth of the cochlea, and those which are high, the 
narrower portions near the apex. In this respect, there- 



How is it kept tei 

ditory nerve is affected ? 



Descril / .86. How is it that the au- 



270 INTERFERENCE OF SOUNDS. 

fore, the function of hearing should have two limits, one 
for low and the other for high notes, as experience proves 
to us is actually the case ; but possibly the scale is, so to 
speak, enlarged through the various degrees of tenseness 
which may be given by the contractions of the cochle- 
aris muscle. A general idea of the nature of this limit- 
ed vibration may be obtained by recalling the effect pro- 
duced when one musical instrument is played in the vi- 
cinity of another, as when, for example, a flute is played 
near to a piano-forte, the strings of the latter are thrown 
into sympathetic vibration, and the piano emits a note 
answering to each note of the flute. All the strings are 
not thrown into vibration at once, but for each note of 
the flute that string of the piano in unison vibrates. 

In the view here presented, I consider that each ex- 
ternal musical note causes a special portion of the spiral 
lamina to vibrate, and that the particular nerve fibril 
supplying that portion is affected thereby, and thus a 
distinct sensation is communicated to the brain, the 
nerve fibrils to the right and left of the one affected ly- 
ing at rest. It may probably be that the denticulate 
structure has for its duty the more perfect production 
of this isolated effect, or that the teeth thereof act like 
the dampers of a musical instrument, and restrain the 
vibration. Notes the wave length of which is great, 
or, what is the same thing, the times of the vibrations 
of which are long, affect those portions of the spiral la- 
mina which are broad and near to the base of the coch- 
lea, but notes whose wave lengths are short, and times 
of vibration correspondingly brief, affect those portions 
near to the apex. But probably the scale is changed, 
as before said, by the tension of the cochlearis muscle, 
and thus the same part of the lamina can take charge 
of a range of many octaves. 

It may be inquired how it is that a sound passing 
through the auditory canal, the bones of the tympanum, 
the membrane of the fenestra ovalis, and thus affecting 
its destined portion of the lamina, does not give rise to 
an idea in the mind of repetition or reverberation by 

Why are there two limits in hearing? What physical illustration 
of the action of the spiral lamina may be given ? What is probably 
the use of the denticulate structure ? How may several octaves be 
perceived ? 



IXTEEFEEENCE OF SOUNDS. 27l 

moving back and forth through the two scala?, and af- 
fecting its proper nerve fibril at each passage. Is there 
not a necessity for the existence of some mechanism of 
interference to destroy the wave after it has once done 
its work ? Admitting the force of such inquiries, we 
can not avoid being impressed with the fact that the 
two scala? of the cochlear tube present all the aspects 
of a mechanism constructed for the discharge of such a 
duty. For interference to take place among undula- 
tions of any kind, waves upon water, sounds in the air, 
or the ethereal undulations constituting light, the essen- 
tial condition is that they shall run through paths of a 
certain unequal length. They must also be brought, 
for a full practical efiect, to their common point of en- 
counter under a very acute angle, and these conditions 
are represented in the scala vestibuli and the scala tym- 
pani, which are of unequal length, placed at such an 
acute angle to one another that they might almost be 
said to be parallel, occupied by a fluid of the same den- 
sity, and through both at the same moment are passing 
the undulations constituting the same sound, one hav- 
ing been communicated by the fenestra ovalis, the other 
through the fenestra rotunda, their common point of 
convergence, and perhaps of mutual destruction, being 
at the helicotrema, the aperture at the apex through 
which they intercommunicate. Xor can we fail to be 
struck by the circumstance, if this explanation of the 
function of the scala? be correct, in what an admirable 
manner the whole instrument is provided with self-ad- 
justing power, since, when the stirrup forces in the 
membrane of the fenestra ovalis, the pressure communi- 
cated through the water pushes out the membrane of 
the fenestra rotunda, and thereby the relative length of 
the two BCalfiB has changed, the one having become lon- 
by as much as the other has become shorter, an ad- 
stment necessary to bring about total interference at 
the helicotrema. And we might add that such a con- 
struction is all the more interesting, for, since it is the 
intensity of the waves that is to be destroyed, reliance 
is had upon the intensity instrument, the drum, to pro- 

What is the function of the Bcalae ? How is the relative length of 

the two scalar made to change? Why is interference of the received 
sound necessary? 



272 STRUCTURE OF THE SEMICIRCULAR CANALS. 

duce that effect, and it is done by the contractions of 
the tensor tympani and stapedius muscles. Perhaps the 
perfect accomplishment of this interference is the stand- 
ard, to which allusion has been made before, by which 
the mind judges of the power put forth by those mus- 
cles, and thereby of the intensity of the sound. 

3d. On the determination of the quality of sounds, the 
structure of the semicircular canals, and their function. 

The semicircular canals are cylindroid tubes, devel- 
oped, as it were, from the vestibule, and of a figure 
which has suggested their name. They are three in 
number, and placed at right angles to one another ; two 
of them are vertical, the third horizontal; they all open 
into the vestibule, the adjacent branches of two of them 
coalescing first. On one of the branches of each of them 
there is a dilatation just before it joins the vestibule; 
to this dilatation the designation of ampulla is given. 
The vestibule of the labyrinth may therefore be regard- 
ed as the common mouth of the semicircular canals, and 
of the scala vestibuli of the cochlea; or, considering its 
order of development, the vestibule may be regarded as 
the essential portion of the labyrinth, and the semicircu- 
lar canals and cochlea appendices that have branched 
forth: from it. 

The vestibule and semicircular canals are lined with 
a membrane which, of course, copies their shape, yet it 
is not in contact with their bony walls, but is parted 
therefrom by a stratum of water ; to this the name of 
perilymph is given ; their interior is also filled with a 
liquid — the endolymph it is called. The bony structure 
is called the bony labyrinth ; this structure is the mem- 
branous labyrinth. A portion of the auditory nerve di- 
vides into three main branches, which present them- 
Fig m 87# selves for the supply of the ampul- 

lae : the brush-like terminations of 
these are accommodated with an 
otolith, or ear-stone. 

Fig. 87 : a, external wall of ves- 
tibule, on which is seen, 5, fenes- 
tra ovalis ; c, fenestra rotunda,. 

Tympanic face of the labyrinth. arj( J 9 ^ tract of the facial nerve ; 

What are the semicircular canals ? What are the perilymph and 
endolymph ? Describe Fig. 87. 




FUNCTION OF THE SEMICIRCULAR CANALS. 273 

(\ superior semicircular canal ; f, posterior semicircular 
canal; ;/, horizontal semicircular canal; i ?, wall of the 
cochlea; t /, aqueduct of cochlea; A', portion of petrous 
bone. 

The explanation usually given of the function of the 
semicircular canals is, that they serve to determine the 
direction of sounds, an idea originating from their re- 
markable rectangular position. However, this is ac- 
complished in almost all cases by directing the external 
canal toward the point from which the sound is coming, 
and judging of its place by the variations of its intensi- 
ty. Animals commonly direct the external ear toward 
the sounding point, guided doubtless in the same way. 
Some physiologists have restricted the use of the semi- 
circular canals to the collection of those sounds which 
strike upon the skull, but, besides the preceding con- 
siderations, there are others derived from comparative 
anatomy indicating that this can scarcely be their duty. 

The intensity of sounds is judged of by the tympan- 
um ; their pitch or wave length is determined by the 
cochlea, and therefore there arises a strong presumption 
that the semicircular canals must have the function of 
distinguishing the third characteristic of sounds, that is, 
their quality ; since, if this be not the case, there seems 
to be no other portion of the auditory mechanism to 
which that office could be assigned. 

The suspicion we are thus led to entertain, that the 
semicircular canals are for appreciating the quality of 
sounds, is strengthened in no common degree by facts 
of comparative physiology. Unfortunately, we know 
so little of the mechanical peculiarity on which distinc- 
tions of quality depend, that we are wholly unable to 
trace out the structural conditions of an organ calcula- 
ted for seizing on them. We know that the quality of 
a note emitted by a violin is different from that emitted 
by a tlute, though the intensity and pitch may be the 
ie, but we can not tell why. In the case before us, 
:i expect no assistance in the way of ar- 
tents from mechanical philosophy, and are limited to 

What i> tl n opinion of the use of the semicircular ca- 

nals? da foi supposing thai they arc really for estima- 

ting the quality of sound-. What is meant by the term quality of 

M 2 



274 COMPARATIVE ANATOMY OF THE EAR. 

the use of those which may be drawn from comparative 
anatomy and physiology. 

Examining, therefore, what appears to be the primi- 
tive plan of the construction of this mechanism, we find 
it to consist of a nerve fibril in connection with an oto- 
lith, or little stony body. Such a construction, included 
in a bag of water, constitutes, in point of fact, the organ 
of hearing of some of the lower tribes, as the gasterop- 
odous molluscs. These animals can have no perception 
of the pitch of sounds or musical notes, and only an im- 
perfect one of intensities. But what they do distinguish 
is one noise from another. Now the idea conveyed to 
the mind by difference of noises is precisely the distinc- 
tion that we are dwelling on, that of quality. 

If, instead of restricting our examination to the semi- 
circular canals, we extend it to the whole organ of hear- 
ing, and consider together, in the case of each animal 
tribe, its requirements, and the manner in which those 
requirements are satisfied, we shall meet with a surpris- 
ing confirmation of the preceding views. The lowest 
requirement we can conceive of is the appreciating of 
noises ; an advance upon this is the determination of 
their direction ; a higher advance, the determination of 
their intensity ; and a still higher, the recognition of 
those combinations of impulses constituting a musical 
sound. For each of these successive requirements the 
auditory mechanism must necessarily become more com- 
plex ; and thus it first appears, as we have just stated, 
as a sac of water, containing a stony grain or otolith 
imbedded in the oesophageal collar. A noise agitates 
the otolith, and by its movement the perception of a 
sound ensues. In cephalopodous mulluscs the auditory 
sac is detached, and the intercommunicating thread rep- 
resents the rudiment of what, in the higher grade of 
development, will be the auditory nerve. With another 
advance the sac is lodged in a cartilaginous cavity. 
Thus, in the cuttle-fish, a simple cartilaginous vestibule 
exists, having within it a membranous bag or auditory 
capsule, filled with fluid, and upon the capsule the fila- 
ments of the auditory nerve are spread. An otolith or 

How may that conclusion be illustrated from comparative anat- 
omy ? Give a general view of the auditory mechanism. Describe 
the comparative anatomy of the ear. 



COMPARATIVE ANATOMY OF THE EAR. 275 

ear-stone is placed within, and this constitutes the entire 
apparatus, while yet there is no vibrating membrane 
and no fenestral aperture. 

Even in still higher conditions the purely mechanical 
character of the structure is manifest, and so, in some 
of those in which the sac opens exteriorly, grains of 
sand, that have been introduced by chance from with- 
out, rest on the hair-like filaments which the auditory 
B&c contains, each filament apparently including a nerve 
fibril. In a still higher condition of advance, as, for ex- 
ample, in the lobster, a portion of the shelly wall form- 
ing the boundary of the auditory cavity is unconsoli- 
dated, and a membrane stretching over the otherwise 
vacant space presents the first rudiment of the fenestra 
ovalis. With the exception of the amphioxus, all verte- 
brated animals have a special organ of hearing, which, 
in successive tribes, presents an interesting increase of 
complexity, beginning in the cyclostomes with a sac in 
the cranial cartilages filled with water, nerve fibrils dis- 
tributed on its wails, and an otolith included, but no ex- 
ternal communicating aperture. From this, in succes- 
sion, the various portions to be developed in perfection 
in the higher races gradually appear; the myxine has 
one semicircular canal arising from the vestibule, the 
lamprey has two, the higher forms have three. As the 
case may be, a portion of the cartilage or bony parietes 
i-; deficient, and, again, the fenestra ovalis is the result. 
Though in the osseous fishes there is neither tympanum 
nor cochlea, in some few the rudiments of the former 

An to exist. The naked amphibia have no cochlea, 
and only one fenestra, answering to the ovalis: to this 
is fitted a stapes ; but in lizards and scaly serpents there 
is a general advance, these having a conical cochlea. 
A- we pass through them the plan is carried out; the 
tympanic cavity and its chain of bones, the Eustachian 
tube, and cochlea appear; and with the rudiment of the 
cochlea there is presented in the tympanic cavity a sec- 
ond aperture, answering to the fenestra rotunda. In 
birdfl the structure offers a continued improvement, com- 
mencing on a plan analogous to that of the scaly amphib- 
ia, but exhibiting a speedy development. The mcm- 

In what order arc the parts of the ear developed in the animal se- 
ries? 



276 COMPARATIVE ANATOMY OF THE EAR. 

brana tympani is composed of several layers; the cavity 
of the drum communicates with cells in the cranial 
bones, the analogues of the mastoid cells ; a bony Eus- 
tachian tube crosses to meet its fellow of the opposite 
side, and open in a common aperture. The ossicles con- 
sist of a malleus, a staff-shaped intermediate bone, and a 
flat stapes, resting on the fenestra ovalis. As if to show 
a tendency to the form it is eventually to assume, this 
bone sometimes presents a forked appearance, the prep- 
aration for a stirrup shape. As regards this bone, birds 
and mammals may be said to overlap, for in its more de- 
veloped condition in birds it bifurcates, but in the lower 
mammals, as the kangaroo, it is still cylindric. * In birds 
of prey the semicircular canals are large, the cochlea 
fairly developed, though as a straight or slightly-curved 
tube, containing its scalse and vibrating lamina : the ves- 
tibule has ear-stones. Through the monotremata this 
condition of construction is continued into the perfect 
mammals : all the aerial tribes have external ears, and 
full development is reached in the auditory mechanism 
of man. 

Now if we collate the facts here presented with the 
requirements of the condition of life demanded by each 
of these successive races, we shall find that the remark 
heretofore made, that the semicircular canals are for the 
recognition of the qualities of sound, is strikingly borne 
out, though, from our ignorance of what it is in which 
quality consists, we are wholly unable to offer an expla- 
nation of the precise mode of action of that part of the 
auditory mechanism. 

We are so prone to extend our ideas of our own per- 
ceptions to the case of other animals that it may not 
here be unprofitable to offer a remark serving to correct 
such views. To many of the sounds we are familiar 
with, birds and other lower tribes are totally deaf; they 
can not appreciate, except within a narrow range, the 
notes of music, and, indeed, to all those in which there 
is no cochlea such notes are inaudible. In the lower 
grades nothing more than a noise can be detected, and 
that doubtless in a very indefinite way. We can there- 
How do these facts bear on the interpretation of the use of the 
semicircular canals? Why is it that all inferior animals are partial- 
ly deaf? 



PERCEPTIONS OF WARMTH. 277 

fore understand how, through imperfection of construc- 
tion, they are cut off from the perception of an infinite 
number of occurrences obvious enough to us. Even 
among our domestic animals, to which we so often speak 
or sing in the way we do to one another, the intellectual 
obtuseness we think we recognize doubtless originates 
in an incapacity to receive those expressions, because of 
faulty structural condition. 



CHAPTER XVI. 
OF VISION. 

Perception of Warmth. — Structure of Ocelli. — Use of 
Lenses. — Physical Principle of the Organ of Vision. 

Description of the Human Eye. — Optical Action of its 
Parts. — Spherical and Chromatic Aberration. — Re- 
ceiving Screen of the Eye is the black Pigment. — 
Long and short Sight, and their Correction. 

Nervous Jleclwnism of the Eye: its Structure and 
Functions. — Manner of Perception by the Petina. — 
Ocular Spectra. — Erect Vision. — Ldea of the Solidity 
of Bodies. 

Accessory Apparatus of the Eye. — The Eye&oics. — 
Eyelids. — Lachrymal Apparatus. 

In the animal series, long before any thing like a dis- 
tinct organ of vision can be detected, there is a percep- 
tion of light and darkness. The hydra, a fresh-water 
polype, offers an example, for this animal seeks the sun- 
ny side of the vessel in which it is placed, preferring it 
to the shade. In the absence of a visual organ, there 
can not be a doubt that its movements depend on the 
perception of warmth, just as when a man who is total- 
ly blind from the sun into the shade, his feelings 
at once notify him of the change. 

Dr. Franklin made an experiment to the following ef- 
fect. He placed on the snow, on a sunshiny winter day, 
pieces of cloth of different colors — black, yellow, white, 
etc.. etc. — in such a position that the sun's rays fell 

What is the first indication of the perception of light? Describe 
Dr. Franklin's experiment. 



278 OPTICAL PRINCIPLES OF THE EYE. 

equally on them. After a certain length of time, on ex- 
amining them, he found that the black cloth had melted 
its way deeply into the snow, the yellow to a less depth, 
and the white scarcely at all. He therefore drew the 
conclusion that, when they are receiving light, surfaces 
become warm in proportion to the depth of their tint, 
and that, of all surfaces, one having a velvety blackness 
is most sensitive, because it can exert the most powerful 
absorbent agency. 

On this principle the ocelli of the lower tribes are con- 
structed. They consist of a collection of pigment gran- 
ules, usually of a red, black, or dark color, seated on the 
expansion of a nervous thread. The principle contained 
in this mechanism is that of relieving the general sur- 
face from the impression of light, or rather of rendering 
it more intense by centralizing it upon a special locality. 
Such a construction involves at once a change in the 
nervous mechanism, by devoting a particular system of 
nerve tubules to the new duty. But, notwithstanding 
this increasing complexity of structure, the physical prin- 
ciple is still as simple as before. It is indeed almost as 
though a blind man should paint upon his skin a black 
space, so that, as in Franklin's experiment, it might be 
more sensitive to the sun. With this devotion to a new 
duty the nervous tubules doubtless assume an isolated 
function, and thus there arises a nerve of special sense. 
The ocelli of the lower animals are sometimes quite nu- 
merous. From this a new power is at once derived, 
the power of determining the position of the source of 
light, a property doubtless becoming more perfectly 
marked in proportion to the number and symmetry of 
arrangement of the ocelli. As we ascend the animal se- 
ries in our examination, we soon find that complexity is 
being introduced. A membranous hood, arising from a 
little fold of the external tegument, shadows forth the 
rudiment of an eyelid, and seems to indicate to us that, 
even in these low grades, the condition we shall event- 
ually find so strikingly marked in the high ones already 
exists, that functional activity involves destruction, and 
that the sensory mechanism must have its period of re- 
pose. 

How are ocelli constructed ? What advantage is gained from hav- 
ing them symmetrically arranged ? 



STRUCTURE OF THE EYE. 279 

Approaching the more highly-developed conditions of 
the organ of vision, we may next consider the cases pre- 
sented" by the eyes of insects and the eyes of higher 
mammalia. In these a new physical principle has been 
introduced, the optical property of the convex lens, a 
transparent solid, having one or both of its surfaces 
curved, and obtaining therefrom the power of forming 
representations, or images of objects in front of it, at a 
certain focal distance behind. 

The instrument known as the camera obscura repre- 
sents the optical construction of the eye. Upon a re- 
ceiving surface or screen, placed at the focal distance 
behind its lens, images are depicted of whatever objects 
may chance to be in front; but — and this is a remark 
of interest to us now — the visual range, or field of view, 
is quite limited. In animals, the perfection of whose 
vision requires that, instead of being restricted in their 
view to a narrow space, they should be able, as it were, 
to take in almost a hemisphere at a glance, this extension 
of the visual function can only be accomplished in one 
of two different ways. To use the illustration we have 
been employing, it may be attained by having innumer- 
able camera pointing in innumerable directions, and 
conveying the resulting images to one common surface; 
or by having one, or at most two, camene set upon a 
movable stand, which can quickly point them in any di- 
rection, and so enable them to inspect successive fields 
of view with almost instantaneous rapidity. The for- 
mer plan is resorted to in most insects, the latter in man. 
In insects, the immobility of the head upon the trunk 
would interfere with any rapid rotation of the visual or- 
gan ; in man, the facility with which rotation can take 
place upon the neck as on an axis, and the movement 
of the eye in its orbit, accomplishes the object without 
any kind of difficulty. 

In continuing an investigation of the structure of the 
eye, it is convenient to consider it under three heads: 
. Its optical mechanism ; 2d. Its nervous mechanism ; 
3d. [ta accessory apparatus. 

What is a convex lens? What ifi meant by it- focal distance? 
Describe the use of the camera obscura. By what methods may an 

increased field of view be obtained? 



280 OPTICAL MECHANISM OF THE EYE. 

1st. Of the Optical Mechanism of the Eye. 

The human eye is of a globular form, and about one 
inch in diameter. It is not perfectly spherical, its later- 
al diameter being shorter than its antero-posterior by 
about one twentieth part. It may be described as con- 
sisting of three coats, which, forming a shell, contain 
transparent media and the optical apparatus. It might 
also be considered as arising from an expansion of the 
optic nerve into an almost spherical cavity, and which, 
being fortified by certain tissues behind, has a dioptric 
mechanism in front. 

The coats of the eye are three in number ; the scle- 
rotic, the choroid, and the retina. The sclerotic is the 
exterior. It is a white fibrous membrane, very tough, 
and possessing the necessary resistance to give mechan- 
ical protection to the parts within. Within this is the 
choroid, a vascular layer or tunic, presenting on its inte- 
rior the black pigment which darkens the interior of the 
eye. The innermost coat is the retina, an expansion of 
the optic nerve. The sclerotic coat is perforated in 
front, and into the circular aperture so arising the trans- 
parent cornea is let, like a watch-glass. Many anato- 
mists, however, consider that the cornea is absolutely 
continuous with the sclerotic, and a part of it ; the scle- 
rotic and the choroid are united round the edge of the 
cornea by the ciliary ligament. The iris is perforated 
in its centre, the aperture being designated as its pupil. 
Posterior to the iris is the crystalline lens, the space be- 
tween the lens and the cornea being filled with the aque- 
ous humor, in which the iris floats, dividing it into two 
regions, called, from their position, the anterior and pos- 
terior chambers. All the rest of the globe between the 
back of the lens and the retina is filled with a substance 
extremely transparent, and known as the vitreous hu- 
mor. The aqueous humor, the crystalline lens, and the 
vitreous humor, by reason of their transparency, offer, 
therefore, no obstacle to the passage of light. 

Fig. 88 : a a, sclerotic, turned over; 5, choroid; c c, 
ciliary nerves traversing sclerotic, and going between it 
and choroid ; J, retina ; 6, vitreous bod y ; f crystalline ; 

What is the form and size of the human eye ? How many coats 
has it ? How are they arranged ? 



STRUCTURE OF THE EYE. 



281 



<7, middle section of iris; A, middle section of cornea; », 
anterior chamber ; j : posterior chamber ; Jc, canal of Fon- 

tana, between the cilia- 
ry circle and iris on one 
side, and sclerotic and 
cornea on the other. 







Profile view of the eye. Front view of the eye. 

Fig. 89; a, transparent cornea ; 5 5, sclerotic ; c, iris; 
c7, pupil ; c, ciliary circle ; f, choroid, on which is seen 
the dichotomous termination of the ciliary nerves; g, 
ciliary processes ; A, crystalline. 

Fig. 90 : a, upper eyelid ; 5, lower eyelid, showing 
the different layers composing them ; c c, conjunctiva, 







reflected from posterior face of eyelid upon the anterior 
face of the globe of the eye; d a, orbito-ooalar aponeu- 

Pescribe Figs. 88, 89, 90. 



282 



STRUCTURE OF THE EYE. 



rosis, prolonged upon 6, the sheath of the optic nerve, 
and sending sheaths to the muscles ; f, the superior rec- 
tus ; g, the inferior rectus ; h h, sclerotic, re-enforced be- 
hind by sheath of optic nerve, and in front by aponeu- 
rotic expansion of recti muscles ; i, transparent cornea, 
cut to show its lamellar texture ; J J, choroid ; &, ciliary 
circle ; /, ciliary body and processes ; m, iris and pupil ; 
n n, canal of Fontana; o o, retina, continuous with sub- 
stance of optic nerve ; p, ciliary circle of Zinn ; q q, hy 
aloid membrane ; r, capsular artery, lodged in hyaloid 
canal ; s s, vitreous humor and its cells ; £, crystalline 
and its capsule ; u u, canal of Petit ; v, anterior cham- 
ber ; as, posterior chamber. 

Fig. 91 : a a, section of sclerotic; 5, exterior surface 
of the choroid, on which are seen, c c, the vasa vortico- 
sa ; d d, ciliary nerves ; e, ciliary ligaments ; f, anterior 
face of iris ; g, pupil. 

Fin. 91. Fig. 92. 




The veins of the choroid. 



The arteries of the choroid. 



Fig. 93. 



Fig. 92 : a a, exterior surface of the choroid and the 
iris, showing the arterial network of these two mem- 
branes, supplied by the ciliary arteries, 
which, after having traversed the scle- 
rotic, divide into b b, posterior ciliariefl 
for the choroid, and c c, anterior cilia- 
ries for the iris. 

In the optical axis of the eye there is 
upon the retina a spot of about the 
twentieth of an inch in diameter, called 
the yellow spot of Soemmering. Its 
position is shown in Fig. 93. The en- 
Describe Figs. 91, 92, 93. 




Yellow spot of Soem- 
mering. 



ITS OPTICAL ACTION. 

trance of the optic nerve is at the spot marked at some 

distance on one side. 

Of the 

It is the province of the works on natural philosophy 
to explain how, when rays of light tali upon a convex 
lens, or upon combinations oi such lenses, an inverted 
image of the object will form at the proper focal dis- 
tance. For the purposes of physiology, it is sufficient 
to receive this as a fact, easily illustrated by observing 
the inverted images of external objects depicted upon a 
sheet of white paper when a convex lens or magnify ing- 
glass is held at a particular distance between the object 
and the paper. 

In making such an experiment, some other tacts inter- 
esting to the physiologist may be readily demonstrated : 
1st. That the focal distance, that is. the distance between 
the lens and the paper, is variable: it is greater for ob- 
's that are near, less for those that are remote: 2d. 
That lenses of different curvatures being compared to- 
gether, the flatter ones have the longest focus for obi 
at the same distance ; 3d. That lenses of the same fc 
but of different dkuneters. give images unequally sharp, 
an indefiniteness being perceived in the image given by 
the lens of large diameter. This indistinctness is due 
to the spherical figure of the lens, and would not have 
occurred had the surface been ground to another conic 
section. It is called spherical aberration; 4th. Un] — 
the lens be of very long focus, or its aperture or diame- 
ter be very small, the edges of the images it yields will 
be fringed with rainbow colors, and thereby a - 
cause of indistinctness arises. It is called chromatic 
aberration. This aberration may b vp- 

erly combining together lenses made of different 
ing media, and with but a f suitable curvature- : a 
combination in which this has been effect I an 

achromatic lens; and if, at the same tin ar- 

ras _ ts, the .1 aberration has I ed, 

rmed aplanatic. 

N w the aqueous humor, bounded by the corr, 

What i> the optical action of a co: mt by 

rical abc: What is meant by chromatic aberrati 

"What ifl an aplanatic le: 



284 THE RECEIVING SCREEN. 

front and the crystalline lens behind, acts as a convex, 
and therefore converging lens, and to this effect the 
crystalline itself adds powerfully, the two conjointly 
causing the images of external objects to form upon the 
black pigment. These images are, of course, inverted. 

The adjustment of the eye for perfect vision of ob- 
jects at different distances is accomplished by the action 
of the ciliary muscle, the requisite movement being to 
draw the lens farther from the black pigment when the 
object is near. There has been a difference of opinion 
as respects the actual screen upon which the images 
form. Some of the early optical writers regarded the 
black pigment as being that receiving surface, an opin- 
ion almost universally abandoned, the function having 
been of late attributed to the retina, but, as it appears 
to me, on totally insufficient grounds. The arguments 
against the retina, both optical and anatomical, are per- 
fectly unanswerable. During life it is a transparent 
medium, as incapable of receiving an image as a sheet 
of clear glass, or the atmospheric air itself; and, as will 
presently be found, when we come to describe its struc- 
ture, its sensory surface is its exterior one, that is, the 
one nearest to the choroid coat. But £he black pigment, 
from its perfect opacity, not only completely absorbs 
the rays of light, turning them, if such a phrase may be 
used, into heat, no matter how faint they may be ; it 
also discharges the well-known duty of darkening the 
interior of the eye, and therefore preventing indistinct- 
ness through the straying of the rays of light. Perfec- 
tion of vision requires that the images should form on a 
mathematical superficies, and not in the midst of a 
transparent medium. The black pigment satisfies that 
condition, the retina does not. 

Spherical aberration is compensated for partly by the 
increasing density of the lens toward its centre, and 
partly by the action of the iris, which stops such rays 
of light as are at any considerable distance from the 
axis of the eye, acting in the same manner as a perfora- 
ted plate or diaphragm in ordinary optical instruments. 

It does not appear that there is any attempt at cor- 

What are the convergent media of the eye? How is adjustment 
for distance accomplished ? What is the receiving screen of the 
eye ? How is spherical aberration corrected ? 



LOXG AND SUOKT SIGHT. 2S5 

recting the chromatic aberration of the eye, though it is 
popularly supposed that the cornea, the aqueous humor, 
the lens, and the vitreous humor act together in the 
same manner as the different pieces of glass in an ach- 
romatic arrangement. Optical reasons, however, found- 
ed upon the constitution and refractive powers of those 
substances, lead us to abandon that view, and in a theo- 
retical respect to regard the eye as imperfect in this 
particular. 

Adjustment for the variable intensity of light is effect- 
ed by the dilatations and contractions of the iris, the 
pupillary opening of which varies from the -^ to the -J 
of an inch in diameter. TTe are thus enabled to bring 
to the same degree of illuminating effect upon the retina 
lights differing in brilliancy in the proportion of one to 
forty-five. 

In what has been said, reference is made to a perfect 
eye ; but imperfections are very common. Two may 
be more particularly pointed out — long-sightedness and 
short-sightedness. In the former, objects, to be seen 
distinctly, must be placed farther off than the usual dis- 
tance ; in the latter they must be brought nearer. Long- 
sightedness arises from the flatness of the lens or cornea, 
so that the focal images given do not fall truly on the 
black pigment, but would be, at a certain distance, ex- 
terior to it ; hence the indistinctness that results. Short- 
sightedness is due to an excess of curvature in the cor- 
nea or lens, the rays forming their focal images before 
the black pigment is reached. The former defect may 
be removed by the use of convex lenses as spectacles, 
the latter by concave. It is often said that short-sight- 
edness is a defect of early life, long-sightedness of old 
age. However this may be in another respect, it is not 
so optically. Indeed, cases sometimes occur in which 
one eye is affected with the former and the other with 
the latter difficulty. Very frequently the two eyes, com- 
pared together, will be found differently advanced in 
their degree of imperfection, and hence the difficulty of 
obtaining a pair of spectacles, though the selection is 
attempted to be made out of a large assortments In 

Is the chromatic aberration corrected? What is the adjusl 
for variation of brig \ v. > long and short sight ? How 

mav thev be corrected? 



286 STRUCTURE OF THE RETINA. 

such cases, each eye should be accommodated with a 
lens to suit itself. 

Compared with the organ of hearing, the eye is much 
more limited in its action ; for, while the ear can distin- 
guish sounds varying through many octaves, the eye 
can only perceive vibrations which, to use the language 
of acoustics, differ by a single octave only. To one 
octave, therefore, its range is limited. 

The eye is limited in another respect; it can not 
simultaneously compare lights differing from one an- 
other in brilliancy if the one should be upward of 64 
times as bright as the other. The more luminous over- 
powers or extinguishes the feebler. We can not see 
the light of a candle if w T e hold it up against the sun. I 
may refer to the experiments I have published, estab- 
lishing that upon this fact is founded the most exact 
method of photometry yet known. 

2d. Of the Nervous Mechanism of the Eye. 

The retina, commonly described as an expansion of 
the optic nerve, intervenes between the vitreous humor 
and the choroid coat. 

Regarding it as composed of distinct layers, the inner- 
most of which, in contact with the hyaloid membrane, 
is called the fibrous gray layer, arises from the tubules 
of the optic nerve, which have cast off the white sub- 
stance of Schwann ; and in passing, we may dwell em- 
phatically upon the point that at that spot, where it ex- 
ists alone, that is to say, where the optic nerve is enter- 
ing the eye, vision can not be performed. Beneath, or 
outside this fibrous layer, comes the gray vesicular lay- 
er : it is analogous to the vesicular matter of the brain. 
The two layers thus far described are served with cap- 
illary blood-vessels of extreme minuteness. Outside of 
the gray vesicular layer is the granular layer, which, as 
its name imports, consists of a congeries of granules, 
probably the origin of the vesicles, new ones arising 
from this layer continually. Yet again, outside of the 
granular layer, comes a delicate sheet, known as the 
membrane of Jacob, but formed, in reality, from the 

What is the limit of vision? What is the limit in variations of 
brightness? Describe the construction of the retina ? What is Ja- 
cob's membrane ? 






NERVOUS MECHANISM OF THE EYE. 287 

juxtaposition of a set of rod-shaped and conical bodies, 
the thicker ends of the rods being outward, the thinner 
inward. 

It is to be particularly remarked that the sentient or 
receiving part of the retina is the posterior, or that which 
is in contact with the black pigment. 

The second pair of nerves, from which the retina is 
thus derived, are, from their function, designated the 
optic nerves. They do not enter the sclerotic in its op- 
tical axis, but at a little distance on one side, and ob- 
liquely — a provision doubtless intended, in a measure, to 
avoid the occurrence of the blind spot on the centre of 
the field of vision, and to place it unsymmetrically in the 
two eyes, so that each eye shall compensate the defect 
of the other. 

Besides the optic nerve, which is exclusively the nerve 
of vision, the collateral parts of the eye are supplied from 
various sources. Of these nerves, the functions are very 
various ; some are for the movement of the ball, or for 
general sensibility of the surface, or for the movements 
of the eyelids, or for those of the iris, and some for the 
lachrymal apparatus. 

Of the Function of the Nervous Mechanism of the Eye. 
Reasons have already been given for considering that 
it is the black pigment which acts as the receiving or 
optical screen, and not the retina. If no other argument 
was adduced for departing from the opinion usually ex- 
pressed, attributing this function to the retina, the thick- 
ness of that structure would be sufficient; images can 
only form with precision or sharpness upon an abrupt 
surface. And since it is now indisputably ascertained 
that both the chemical effect and the heating effect of 
the rays of light depend upon their absorption, those 
effects being in direct proportion to the completeness 
of the absorption, we are justified in inferring that, since 
the eye is sensible to rays of a very low intensity, and to 
each of the colored ones equally, its screen of reception 
must not only be a superficies, but likewise a black one. 
Such a surface the black pigment is. In the case of al- 

Which layer of the retina u Its sensitive one? How are the optic 
nerves arranged? "What other nerre supplies an- given to the eve? 
How is it certain that the black pigment is the receiving sur: 



288 NERVOUS MECHANISM OF THE EYE. 

binos, and animals having the black pigment imperfectly 
developed, the receiving surface or screen is still the in- 
terior of the choroid. Under such circumstances, vision 
must be indistinct. 

Recalling what has been said respecting the diffuse 
sensibility of the lower members of the animal series to 
light, and the structure of ocelli, it accords well there- 
with to consider that the primary effect of the rays of 
light upon the black pigment is to raise its temperature, 
and this to a degree in relation to their intensity and in- 
trinsic color; light of a yellow tint exerting, as has been 
said, the most energetic action, and rays corresponding 
to the extreme red and the extreme violet the feeblest. 
The varied images of external objects thus painted upon 
the black pigment raise its temperature in becoming ex- 
tinguished, and that in the order of their brilliancy and 
color ; the pigment thus discharging a double duty, as 
a surface of extreme sensibility for calorific impressions, 
and also as darkening the interior of the globe. 

In this local disturbance of temperature, in my opinion, 
the act of vision commences, this doctrine being in per- 
fect harmony with the anatomical structure of the retina, 
the posterior surface of which is its sensory surface, and 
not the anterior, as it ought to be if the explanation usu- 
ally given of the nature of vision be correct; and there- 
fore, as when we pass the tip of the finger over the sur- 
faces of bodies, and recognize warm and cold spaces there- 
upon, the same occurs with infinitely more delicacy in the 
eye. The club-shaped particles of Jacob's membrane are 
truly tactile organs, which communicate to the sensory 
surface of the retina the condition of temperature of the 
black pigment. 

But this communication of a variation of temperature 
implies a variation in the waste and repair of the retina 
itself, for there can be no doubt that all such changes are 
accelerated by an increase of heat, and diminished by its 
decrease. And though in this manner the origin of the 
action which has been set up is calorific, and therefore 
physical, it immediately becomes converted into a physi- 
ological equivalent in the metamorphosis and destruction 
of a nervous tissue. 

What is the effect of heat upon it ? Describe the mode of percep- 
tion by the retina ? 






FUNCTION OF THE RETINA AND CIIOKOID. 289 

The eye can not perceive rays coming from a source 
the temperature of which is lower than 1000° F., for such 
rays can not pass through a stratum of water or through 
the humors of the eye. Natural philosophers, in making 
a distinction between light and heat, have too often over- 
looked the fact that, though thermometers are sensitive 
to rays of every sort, the eye is not. Its indications are 
complicated by the necessary introduction of absorbent 
media, which stop all rays of low refrangibility. 

The impression arising from the disturbed condition 
of the retinal vesicles is carried by the optic tubules to 
the chiasm of the two nerves. Apart from the general 
facts elsewhere presented by physiology, the existence 
of a blind spot at the entrance of the optic nerve, w T here 
there is a necessary absence of vesicular structure, is a 
clear proof of the insensibility of the tubular structure to 
the influence of light. Considering, therefore, the retina 
as typically composed of three layers, one of tubules, one 
of vesicles, and one of granules, and these in health being 
perfectly transparent, the luminous beams pass through 
them just as they do through the atmosphere, without 
exerting the slightest effect ; and as, when those rays 
strike the opaque surface of the earth, or are absorbed 
by the sea, heat is disengaged and effects ensue, so like- 
wise, when they have reached the black pigment, the 
changes I have been designating arise. The vesicular 
layer undergoes rapid metamorphosis, the effect of that 
change is transmitted by the tubular layer, and in the 
granular the germs are constantly arising from which 
the waste of the middle layer is repaired. So, therefore, 
the tubular layer is for conduction, the vesicular layer for 
waste, the granular layer for repair; and now appears 
the significance of the construction and proximity of the 
choroid coat, for the waste of the vesicular layer can not 
occur save under the oxidizing influence of the arterial 
blood, nor can the nutrition of the granular layer be ac- 
complished except under the same condition. Moreover, 
the resulting products of waste require to be quickly re- 
moved, and it is not possible to conceive the construction 
of an arrangement better adapted for this triple object 

Why can not the eye perceive raya issuiog from a source lower than 
1000°? What is the function of the two chief layers of tko retina 
and of the choroid ? 

N 



290 SINGLE VISION. 

than that which the choroid presents. On the old view 
of the nature of vision, the construction of the choroid 
seems to be without significance. 

The effect thus communicated to the vesicular layer 
of the retina, through the intervention of Jacob's rods 
and cones, is now carried along the nervous tubules out 
of the globe of the eye. The nerves from each eye, con- 
verging, encounter one another at the chiasm. Here it 
is, however, to be understood that, while the proper op- 
tic tubules of the right eye go to the left brain, and of 
the left eye to the right brain, the anterior band of com- 
missural tubules brings the two eyes into a special rela- 
tion with one another, the right side of one eye corre- 
sponding with the right of the other, and the left with 
the left; or, to put the same statement undef a more sim- 
ple yet more instructive form, the outer side of one eye 
corresponds with the inner of the other, and in this man- 
ner the two retinae become as if they were virtually in- 
cased the one within the shell of the other, an arrange- 
ment obviously compensating in a degree for the blind 
spot of each eye, and, indeed, eliminating the effect of all 
accidental irregularities, for numberless such irregulari- 
ties must exist, there being a necessity, for example, that 
blood-vessels should cross through the sensitive to the 
conducting structures, and such blood-vessels give rise 
to lines of inertness. 

From this commissural arrangement it comes to pass 
that each retina possesses regions of symmetry with the 
other, and on this singleness of vision depends ; each 
point of the outer portion of the retina of the right eye 
has its point of symmetry in an inner portion of the left, 
and when from a distant object rays fall on these sym- 
metrical points, that object will be seen single; but if, 
by the pressure of the finger or otherwise, we compel 
the image to fall in one of the eyes upon another, and, 
therefore, non-symmetrical point, the object at once be- 
comes double. It should be remarked that this exchange 
of symmetry concerns only the lateral divisions, for the 
upper portion of one eye corresponds with the upper 
portion of the other, and the lower with the lower. 

Impressions made upon the retina do not disappear 

Describe the interconnection between the right and left eye. What 
is its result ? Explain the cause of single and double vision. 



ERECT VISION — THE STEREOSCOPE. 291 

instantly, but gradually fade away, and in so doing oc- 
cupy a certain period of time, varying with the bright- 
ness of the original light, the existing condition of the 
eye, and the illumination to which it is exposed. This 
duration of impressions is commonly estimated at about 
one third of a second. It is a phenomenon analogous 
to that of the continuance of sound in the ear, and sub- 
serves an important purpose of keeping vision continu- 
ous and distinct during the winking of the eyelids. 
Commonly it is illustrated by referring to the familiar 
experiment of a stick lighted at one end and twirled 
rapidly round, which gives rise to the appearance of a 
continuous fiery circle. Many ingenious and interesting 
toys, such as the thaumatrope or wonder-turner, act on 
this principle. 

There have been few optical problems more warmly 
contested than that of erect vision. The image at the 
bottom of the eye is inverted, but we see the object up- 
right. Some have supposed that we really see things 
upside down, but have learned to correct the 'error by 
the sense of touch. Doubtless the true explanation is 
to be found in the anatomical construction of the eye. 
It should be borne in mind that there is a very wide 
difference between the image formed at the bottom of 
an eye as we look at it, and, if such an expression may 
be used, as the eye itself looks at it. We see it from 
behiud, the retina sees it from the front. 

The stereoscope shows to what an extent our ideas 
of the solidity of objects depend on the differences of the 
images in each eye. By reason of their difference of po- 
sition, each of the two eyes will have a different picture 
upon its black pigment of any solid object, and the mind, 
combining these dissimilar pictures into one, gathers 
therefrom the idea of solidity. If thus we offer to the 
eyes two pictures of a given object, presenting the same 
form as that object would have done when seen from 
each eye respectively, the mind combines these fiat pic- 
tures together, and can not divest itself of the idea of a 
solid body. This is the principle of the stereoscope. 

The eye is adjusted to the varying intensities of light 

What ia the duration of impressions on the eye? fa any tiling 
known with certainty a 3 to erect vision? On what principle docs the 

btereoscopo depend ? 



292 SUBJECTIVE IMAGES. 

by the motions of the iris, which admits more or fewer 
rays according to its state of contraction, an action, on 
certain occasions, aided by the orbicularis palpebrarum, 
which, by bringing the eyelids together, limits the num- 
ber of rays passing to the pupil. 

Although many images may be simultaneously exist- 
ing upon the retina, the mind possesses the power of 
singling any one of them out and fastening attention 
upon it, just as among a number of musical instruments 
simultaneously played, one, and that perhaps the feeblest, 
may be selected, and its notes exclusively followed. 
These phenomena, however, are not dependent upon any 
peculiarity of construction of any of the organs of sense; 
and as the mind can perceive the images of external 
things, so can it give rise to spectral illusions which may 
simulate perfectly the aspect of external forms. The 
anecdotes of such occurrences found among all people 
are not the fabrications commonly supposed. The mind 
can be readily deceived, even in spite of itself, as the 
phenomena of the stereoscope prove ; and spectres, hav- 
ing their origin in natural or diseased conditions of the 
brain, may accurately replace images that have been 
painted in the eye. It is said, however, that we may 
readily distinguish, by means of a simple optical test, a 
true external apparition, if any exists, from a phantom 
of diseased imagination; for by pressing duly with the 
finger on the ball of one of the eyes, external objects are 
at once doubled, but it is not so with a mental illusion ; 
and we may therefore suspect that, even in the best au- 
thenticated cases of the appearances of these unnatural 
forms, had this test been applied, their true character 
would have been ascertained ; and that, since none of 
them would have undergone duplication, they would at 
once have been detected as mere hallucinations of the 
mind. 

It is to be understood that the sensation of light is 
purely mental, and whatever can disturb the nutrition 
or waste of the retina will give rise to luminous impres- 
sions. The pressure of the finger on the ball of the eye, 
a blow, the passage of an electric current, and divers 

What is the nature of ocular spectra and subjective images ? What 
test is there for them ? How is it known that the sensation of light 
is purely mental? 



THE EYEBROWS AND EYELIDS. 293 

other causes, will at once produce the appearance of 
light, and even of colors. Heat is only one out of a mul- 
titude of agents that can disturb the retina. 

3tf. Of the Accessory Apparatus of the Eye. 

The accessory apparatus of the eye consists chiefly of 
the eyebrows, the eyelids, the Meibomian glands, the 
lachrymal mechanism, and the muscles for the move- 
ment of the ball. 

The eyebrows are two arches of integument, covered 
with hair, on the upper edge of the orbit. They are 
usually classed with the appendages of the eye upon 
the supposition that they protect that organ from undue 
intensity of light, or preserve it from the ingress of 
drops of sweat. They aid greatly in the expression of 
mental emotions, but perhaps should rather be looked 
upon as among the remaining vestiges of the hairy teg- 
ument affording a protection to the entire skin of other 
mammals below man in the animal series. Th^e eyelids 
may be described as a pair of valves, the upper one hav- 
ing a much greater latitude of motion than the lower. 
Their use is to afford protection to the eye by closing 
entirely over it, more particularly during sleep ; to keep 
its optical surface moist and free from dust by their 
winking motion. They are brought into action by the 
contact of air or of irritating particles, through the fibres 
of the fifth and facial nerves, or by the agency of light 
upon the retina. The edges of the lids are furnished 
with rows of curved hairs, the eyelashes, adding greatly 
to the protection of the delicate organ beneath, w T hile 
permitting vision to take place to a certain extent. 
Opening upon the edges of the eyelids are the foramina 
of the Meibomian glands, in the upper lid there being 
about thirty, in the lower somewhat fewer. The glands 
themselves are imbedded on the internal surface of the 
cartilage of the lids, and afford an oily secretion, to dis- 
charge the double duty of preventing adhesion of the 
lids, and, by its relation of capillary attraction, hinder- 
ing the overflow of the water which moistens the eye 
upon the cheek. 

Of the lachrymal apparatus, it may be said that in the 

Of what docs the accessory apparatus of the eve consist? What is 
the use of the eyebrows ? What is the use of the eyelids? 



294 THE LACHRYMAL APPARATUS. 

same manner that we breathe upon a spectacle glass 
and wipe it that its surface may be perfectly clean, so it 
is necessary for the optical action of the cornea that its 
surface should be constantly washed, and even more so, 
for its lamellated structure is such that, if it be not kept 
constantly damp, it loses much of its transparency. This 
therefore renders it necessary that there should be a 
mechanism for the supply of water, another for spread- 
ing that water uniformly over the surface of the cornea, 
and a waste-pipe for carrying any surplus away. The 
lachrymal gland discharges the first of these duties. It 
is situated in the upper and outer angle of the orbit; its 
secretion, a bitter and somewhat saline water, is brought 
to the surface of the conjunctiva by eight or ten little 
ducts arranged in a row for the purpose of equalizing 
their discharge. The spreading of this fluid over the 
eye, and the simultaneous wiping of the surface, is ac- 
complished by the eyelids. Usually the water that has 
been employed is dissipated by evaporation into the air ; 
but if, by reason of meteorological circumstances, such 
as the dampness of the atmosphere, or by the supply be- 
ing too abundant, there should arise an excess, it is car- 
ried off through two minute orifices upon the edge of 
the eyelids, the puncta lachrymalia. These draw off any 
collection of water that may have accumulated in the 
lachrymal lake, and, carrying it into the lachrymal sac, 
discharge it through the nasal duct into the cavity of 
the nose. From this it is removed by evaporation, the 
current of air alternately introduced and expired afford- 
ing the means of accomplishing that object in a remark- 
able manner. But should the discharge of water from 
the lachrymal gland become excessive, as in weeping, 
this draining mechanism is insufficient, and the water is 
discharged as tears down the cheek. 

Describe the lachrymal apparatus. In what manner does it op- 
erate ? 



OF TOUCH. 295 



CHAPTER XVII. 

OF TOUCH. 

Functions of the tactile Mechanism : its Structure. — Re- 
gions of different Sensitiveness. — Perception of Tem- 
xxture* 

The tactile organ is the skin, or some part, modifica- 
tion, or appendage of it. The general functions of the 
skin have been already described. It remains to speak 
of it in connection with the sense of touch. 

In man, the skin possesses tactility to a different de- 
gree in different regions. On the tips of the fingers and 
on the lips the sensory perception is most acute, while 
it is at a minimum on the trunk and thigh. Its proper 
organ is to be regarded as arising from a concentration 
of general sensibility of the skin upon a special construc- 
tion, the papillary body, as it is termed. The organs of 
vision and hearing consist essentially of two portions, a 
receiving and a nervous, the former being constructed 
on the principles of optics in the one case, and of acous- 
tics in the other. A similar doubleness of structure may 
be recognized in the instance now before us, though 
with a difference of effect, for in those cases the outer 
or receiving organ is for the purpose of more powerfully 
concentrating the influence received, but in touch it is 
the reverse. The office of the cuticle, which covers over 
the true skin, is to render it less sensitive to external im- 
pressions, and for this reason, therefore, it varies in thick- 

18 in different regions, being less developed on those 
portions that are more particularly devoted to tactile 
ability. Considering the hand, or, perhaps, more 
correctly, the tips of the fingers, as being chiefly de- 
voted to the purposes of touch, no construction could be 
conceived of better adapted to that end. Placed at the 
extremity of the arm, a lever jointed at its middle, the 

Does the skin posses equal fertility in all its parts? What U the 
function of the pupillary body? What doobleneai of structure may- 
be observed in the skin? Describe the general construction of the 
organ of prehension. 



296 THE OEGAN OF TOUCH. 

elbow, and the fore part of which has a motion of par- 
tial rotation, pronation, and supination upon its own 
axis, the hand being carried so that its palm presents 
upward or downward, or in any of the intermediate po- 
sitions included in the half - circular motion — jointed 
again by the bones of the wrist, so as to obtain a hinge- 
like movement, the hand may be flexed or extended al- 
most 180 degrees upon the forearm. Its bony struc- 
ture, subdivided into suitable pieces, is clothed with a 
multitude of muscles or their tendons. In the fingers 
and thumb the structure breaks up into five separate 
pieces, possessed of an incredible firmness when we con- 
sider the numberless motions accomplished. The posi- 
tion and articulation of the thumb, enabling it to set it- 
self in opposition to the other four digits, a feature con- 
stituting a hand, properly speaking, gives the power of 
grasping things perfectly, and makes the whole organ a 
perfect mechanism of prehension. The papillary struc- 
ture, developed in its utmost refinement on the tips of 
the fingers, and fortified behind by the nails, which pre- 
sent moderate resistance to pressures, completes this 
contrivance. There have been authors who have assert- 
ed that the superiority of man over other animals may 
be entirely accounted for by his possession of a hand — 
a statement which, though it can not be maintained in 
its generality, is yet a very good proof of the apprecia- 
tion in which this wonderful instrument is held by those 
who have studied its construction and functions most 
closely. 

Between the indications that have to be dealt with by 
the hand as an organ of touch, and those dealt with by 
the eye, there is an essential difference. The eye, for 
example, receives the pictures of external objects upon 
a surface, but the hand examines the solidity of bodies. 
The former is occupied with length and breadth ; the 
latter with all three dimensions, length, breadth, and 
thickness conjointly. 

The mechanism for touch, as distinguished from the 
general dermoid sensibility, is the papillae. They may 
be described as conical eminences on the cutis, at once 

What is the essential construction of the hand ? In what respect 
is there a difference between touch* and sight ? Describe the struc- 
ture of the papillae. 



THE TAPILLJE. 297 

solid and flexible, sometimes clavate in form, and some- 
times having numerous points. They are about the y^- 
of an inch in height, and the -^^ of an inch in diameter 
at their base, these dimensions varying, however, very 
greatly with the situation. They contain a loop of blood- 
vessels and a twig of a sensory nerve, for all the centrip- 
etal nerves, with the exception of those devoted to the 
special senses, may be regarded as concerned in this func- 
tion. The papillae contain an elastic substauce — axile 
body, as it is termed — serving to heighten the sense, 
and the yielding structure of the skin aids in the same 
effect. The papillae are covered over with the cuticle, 
through which, therefore, all action on them must take 
place. 

Fig. 94 represents simple papillae of the palm, the cu- 
ticle having been detached. Fig. 95, compound papilla?, 
with two, three, or four points: a, base of a papilla; b b b, 
separate processes; c c <?, processes of papilla? whose bases 
are not visible. 



Fig. 95. 




Simple p ipillpc, magnified 35 di- 
ameters. Compound papillae, magnified 00 diameters. 

The mode in which the nerve fibre terminates in the 
papilla is as yet doubtful, some asserting that it is ar- 
ranged as a returning loop, and some that it is by a 
pointed extremity. 

The sensitiveness of a part is in proportion to the 
number of papillae it contains. Tables have been con- 
structed setting forth the relations of different regions, 

determined by placing a pair of compasses, the points 
of which were covered with cork, on the parts to be 
tried, the eyes being shut, and closing the compasses un- 
til the pieces of cork could no longer be distinguished as 
separate. It appears that this will take place on the tip 
of the tongue when the points are the ^ T of an inch apart; 

How may the BensiftiYeiieaa of a part be measured? 
N 2 



298 FEELING AND TOUCHING — TICKLING. 

on the tip of the third phalanx, at the -^ of an inch ; on 
the lips, the one sixth of an inch ; tip of the great toe, 
half an inch ; the lower part of the occiput, 1 inch ; and 
on the middle of the thigh, 2\ inches. 

Our estimates of the hardness and softness, rough- 
ness and smoothness of bodies, is primarily dependent 
on indications derived from the sense of touch. We 
should make a distinction, however, between feeling and 
touching, the former being essentially passive, the latter 
active ; and though we usually suppose that, of all our 
senses, touch is the most reliable, it often conveys to 
the mind illusory impressions, as, for instance, in the 
well-known experiment of Aristotle, when the tips of 
the fingers are crossed over each other, and a pea rolled 
beneath them, it seems as if there were two peas,one 
under each finger. The indications of touch are gener- 
ally more correct than those of feeling. Thus, if we 
close our eyes, and another person moves the tip of our 
finger over an unknown surface, he can completely de- 
ceive us by duly varying the pressure, and make us be- 
lieve that it is concave or convex, whereas it may be 
flat ; but if we pass our fingers over the surface our- 
selves, we very quickly come to a true conclusion, be- 
cause now we are conscious of the exertion of muscular 
power ; and from what has been said respecting hear- 
ing, we may infer how delicate our estimate of muscular 
exertion is. The former is therefore an example of 
feeling, the latter of touch. 

Connected with this distinction are the singular phe- 
nomena of tickling; the regions most readily affected 
by this are those of low tactile sensibility. A person 
can not tickle himself, though it is said that cases are 
upon record in which one has been tickled to death by 
another. 

Besides affording an estimate of external pressures, 
the sensory organ enables us to discover variations of 
temperature. It may therefore be thus effected by bod- 
ies upon contact or by bodies at a distance ; and though 
we usually confound the two indications together, there 
is, in reality, a distinction between them ; thus, in cer- 
tain conditions of paralysis, the indications of the con- 

What is the distinction between feeling and touching ? What is 
Aristotle's experiment ? 



OF SMELLING. 200 

tact of bodies may remain, but those of heat and cold 
may have totally disappeared. On examining a surface 
from which the skin has been removed, it does not ap- 
pear capable of distinguishing hot from cold bodies, but 
only communicates to the mind an indefinite sensation 
of pain ; nor can we create sensations of heat or cold 
by any irritation of the nerves. The measure of tem- 
perature by the agency of the skin is very far from be- 
ing exact, as is proved by the simple experiment of 
dipping the finger into very warm water, and then the 
whole hand into water many degrees cooler. The in- 
creased extent of surface seems to overcompensate for 
the lower temperature, and we come to the erroneous 
conclusion that the cooler specimen is the warmer of 
the two samples. 

As sounds may be heard which have no reality, but 
merely originate in the brain, or spectral illusions may 
be seen, so the sense of touch is subject to similar hal- 
lucinations, as a sensation of pressure or weight, or the 
crawling of insects on the skin ; and though we can not, 
by artificial irritation of the nerves, give rise to impres- 
sions of heat and cold, those effects very frequently oc- 
cur in this interior or subjective way. 



CHAPTER XVIII. 

OF SMELLING. 

Structure of the Organ of Smell. — Its proper Instrument 
the First Pair of Nerves, — Limited Region of Smell. 
— Duration of Odors. — Subjective Odors. 

By the sense of smell we are able to distinguish many 
gaseous and vaporous substances from one another. 
They enter the nostrils with the respiratory current, and 
are brought in contact with the olfactory or Schneiderian 
membrane. Though received at first in the elastic state, 
they become dissolved in the mucus moistening that 
membrane. It does not follow, however, that all vapor- 
Is the measure of t e m p erature by tbe skin correct? . Can subjec- 
tive sensations oC touch occur? What is the mode of action of 
odors ? 



300 



THE OLFACTORY ORGAN. 



ous substances give rise to the perception of an odor ; 
for example, water itself communicates no sensation 
whatever. 

The general principle involved in the construction of 
the organ of smell is to expose an extensive and con- 
stantly moistened surface to the air brought in by the 
respiratory current. Of course, other things being 
equal, the larger the surface, the more perfect the sense. 
The object of gaining a great extent of superficial ex- 
posure under a relatively small volume is accomplished 
by spreading the sensitive mucous membrane on pro- 
jections or shelves, which also serve the purpose of in- 
tercepting the incoming current of air. 

The nose, thus constituting the commencement of the 
respiratory tract, forms a characteristic feature of the 
countenance. It is composed in part of bones and in 
part of cartilages, covered over with muscles and integu- 
ment. Its five cartilages give to it shape in its inferior 
portion, and, by their elasticity, enable it to resist ex- 
ternal injury. The whole surface of the nasal cavities 
is covered over with mucous membrane, to which the 
names of pituitary or Schneiderian membrane have been 
given. This mucous membrane likewise extends into 
the maxillary antrum, ethmoid, and sphenoid cells, or 
sinuses adjacent, and opening into the same nasal cavity. 
The Schneiderian membrane is highly vascular, and re- 
ceives its nervous supply from the nasal branches of the 
fifth pair, which give it common sensibility, but its ol- 
factory function depends on the distribution a certain 
portion of it receives from the first, or olfactory nerve. 

Fig. 96. Fig.97. Fig. 96 jllllS-. 

Mpgtojt /jLV trates the distri- 

bution of the ol- 
factory nerve on 
the septum of the 
nose. Fig. 97 is 
its distribution on 
the outer wall of 
the nasal fossa. 
That the function of the first pair of nerves is olfac- 

What is the general principle of construction of the olfactory or- 
gan ? Of what portions is the nose composed ? What is the Schnei- 
derian membrane? Which pair of nerves is the olfactory? 




THE OLFACTORY NERVES. 301 

tory is proved by many facts. Animals in which these 
nerves have been divided are no longer affected by odors 
of any kind, and, generally speaking, the greater the de- 
velopment of these nerves, the acuter is the sense of 
smell. In persons in whom this sense has been defective 
or totally absent, or in those who have been troubled 
with unpleasant odors of a subjective kind, post-mortem 
examinations have shown a corresponding absence or 
lesion of these nerves. 

Id man, the proper olfactory organ is formed by the 
distribution of the olfactory, or first pair of nerves, on 
the mucous membrane covering the upper part of the 
nose, the internal set of filaments being disposed on that 
of the septum, the external on that of the superior and 
middle spongy bones. The membrane is very vascular, 
and covered with a thick, pulpy epithelium. The fila- 
ments distributed to it have lost the white substance of 
Schwann. It is those parts alone to which these fila- 
ments are distributed which possess the sense of smell. 
It seems to be necessary for the vaporous or gaseous 
substances to be dissolved in the moisture covering the 
olfactory membrane in order to their exerting a proper 
effect. If, by chance, the membrane be too dry, the sense 
of smell is temporarily lost, and the same likewise oc- 
curs if it be unusually moist. 

From the mode of distribution of the olfactory nerve, 
it follows that the sense of smelling is restricted to the 
upper portion of the nasal cavity; and, for this reason, 
when we desire to detect odors with unusual precision, 
the air is drawn violently into that region by sniffing. 
On the contrary, we avoid the perception of odors by 
breathing through the mouth, or, as the common phrase 
i-. by holding the nose. 

In one respect there is a striking difference between 
this .Mid vision and hearing. We can perceive 

many luminous impressions at the same time, or bear 
many sounds in rapid succession ; but not so with odors. 
We can smell only one thing at a time, or, at all events, 
the impression remains long upon the olfactory appara- 
tus, perliap- tic- odoriferous substance remains 

How arc the olfactory norvc^ distributed? To what portion of 
the nasal cnxr t* smell restricted? What i- the cause 

of the duration of o<. 



302 OF TASTE. 

dissolved in the attached moisture. The identification 
of substances by their odor necessarily implies a resort 
to recollection or memory, and sometimes we have to ap- 
ply the fragrant object again and again to the nose be- 
fore we can recall with satisfactory precision its name. 
Diseases of the central organs will sometimes give rise 
to the perception of subjective odors, just as they do to 
spectral illusions or sounds in the ears. 



CHAPTER XIX. 

OF TASTE. 

Conditions for Taste. — Structure and Functions of 
the Tongue. — Tactile and Gustative Regions of the 
Tongue. — Complementary Tastes. 

Though the function is participated in by other por- 
tions of the oral cavity, the tongue is to be regarded as 
the organ of taste. The physical conditions under which 
savors are perceived is that the substance shall be pre- 
sented in solution in water, or, at all events, in the saliva. 
From vision, hearing, and smell, the sense of taste differs 
in the circumstance that it requires the contact of the 
acting body. 

Sensations of taste are very frequently conjoined with 
olfactory perceptions, so that we mistake the one for the 
other. There are many substances, reputed to have a 
powerful flavor, which become tasteless when the nose is 
held ; and this remark applies more particularly to such 
as are at the same time volatile and soluble in water. 

The idea of taste may arise irrespectively of the pres- 
ence of any actual substance. A sharp blow will pro- 
duce it, as also the passage of a feeble voltaic current. 
A narrow jet of air directed upon the tongue causes a 
taste resembling that of saltpetre. If the tongue be dry 
and parched, its power of discriminating tastes is greatly 
enfeebled, and the same thing takes place if its tempera- 
ture is very much changed, either by elevation or depres- 

Can subjective odors occur ? What is the physical condition for 
the perception of tastes ? How may that be related to the perception 
of odors ? Give instances of the production of tastes by incidental 
agents. 



STKUCTUKE OF TIIE PAPILLAE OF TASTE. 



303 



sion, as by keeping it for a short time in contact with hot 
or very cold water. 

The action of the tongue, as the organ of taste, de- 
pends upon the papilla* on its surface. These structures 
give to the upper portion of the tongue its rough ap- 
pearance. They are of three kinds : 1st. The conical 
papilla?, which are the most numerous ; 2d. The circum- 
vallate papillae, situate near the base of the organ, and 
from tt 1 ^ to yV of an inch in diameter, with a crater-like 
depression, round the edge of which is a groove, and 
again a circular elevation ; 3d. The fungiform papillae, 
which are chiefly on the sides and tip, their shape being 
conical, the narrow end of the cone being downward. 
The epithelium of the tongue is less dense over the fun- 
giform papilla?, and hence their projecting appearance : 
it is more dense over the conical papillae, and projects 
from them in processes presenting an aspect like that of 
hairs. Some of them contain hair-tubes. Besides these, 
the surface of the tongue has a papillary structure re- 
sembling that of the skin — secondary papillae, as they 
are termed. It is supposed that the conical papilla? are 
chiefly organs of prehension ; the others are organs of 
taste, but that function is participated in by other por- 
tions of the surface of the mouth, as, for example, the 
soft palate, its arches, and the f;?. os. 

tonsils. 

Fig. 98 represents the sur- 
face of the tongue and the ad- 
jacent parts : a a, lingual pa- 
pilla? ; b 5, circum vail ate pa- 
pilla*, disposed along two con- 
rine lines forming the lin- 
gual Y ; '*, foramen cacum ; 
d d) fungiform papillae ; e e, 
filiform papilla ; J] franum 
epiglottidifl ; //, epiglottis ; //, 
anterior pillar of velum ; £, 
sty]' Innus of 

the ; . ///, uvula ; ?/, ve- 

lum pendulum palati ; o, hard 
palate : />. raphe ; 7 7, ori- 
fices of the 1 y ducts Tii. i 




How many Idndfl of papillae baa the tongue? Describe Fig. 98, 



304 THE SURFACE OF THE TONGUE. 

of the palatine glands; r, palatine glands, the mucous 
membrane being removed ; s, palatine glandules ; £, mu- 
cous membrane covering the same glands ; u^ palatine 
tubercle; v v, section of the lower jaw. 

The organ of taste is placed at the commencement of 
the digestive canal ; hence the characters of substances 
may be examined with deliberation while they are yet 
under the control of the will, for when once a body has 
entered the oesophagus it is swallowed involuntarily. 
The tongue, therefore, gives warning of the presence of 
deleterious substances, and in no small degree excites 
the appetite by receiving the impression of pleasant fla- 
vors. The essential condition under which it acts is a 
moist state of its surface, for the dry tongue, though it 
enjoys common sensibility, after the manner of any por- 
tion of the external tegument, does not enjoy taste. 
One of the duties of the salivary glands is incidentally 
to maintain this moistened condition. To a certain de- 
gree,, taste may be regarded as a refinement on touch. 

The surface of the tongue presents the tactile and 
gustative powers in an inverse manner. Examined by 
the method described in the chapter on touch, the com- 
passes must be opened to a great extent, as we pass 
from the tip toward the back of the tongue, in order 
that a double impression may be perceived. This con- 
dition appears to be in accordance with the requirements 
of the organ, common tactile sensibility being most nec- 
essary at its outer extremity, and this gradually passing 
off into the refinement of taste. The action of any given 
substance may be increased by motion and pressure, as 
when it is rolled over the tongue, or held thereby. Its 
sense of discrimination may be rendered more acute by 
education. 

As with the organs of the other senses, so with this, 
an impression made upon it does not instantaneously 
cease, but remains for a certain period of time, indeed, 
in this instance longer than in those. Hence many sub- 
stances acting in rapid succession give rise to a confused 
effect, though it is said that, out of such interminglings, 
an accomplished epicure can fasten his attention on one, 

What are the uses of the sense of taste ? Which are the tactile 
and which the gustative regions of the tongue ? Is it possible to sin- 
gle out one taste from many others ? 



ANIMAL MOTION. 305 

and continue to recognize it just as we recognize and 
follow the sound of one instrument in an orchestra. No 
explanation has as yet been given of the manner of action 
of different tastes, though it is asserted that some act 
upon one, and some upon another set of the papillae. 
After-tastes are also observed, occasionally of a comple- 
mentary kind, as, for instance, the intensely bitter taste 
of tannin is followed by a sweetness. These after effects 
modify the taste of substances taken while they last. 
They therefore form an ample subject for the profound 
contemplation of the epicure, and should occupy the se- 
rious attention of the cook. They may be illustrated in 
a general manner by the injurious effect of sweet sub- 
stances upon the flavour of delicate wines. 



CHAPTER XX. 

OF ANIMAL MOTION. 

Ciliary and Muscular Motion, — Description of Cilia. 

Muscular Fibre : Its Forms , Non-striated and Striated. 
— Muscle Juice. — Manner df Contraction of a Mus- 
cle: its simply of Blood-vessels and Nerves. — Dura- 
tion of Contractility. 

Doctrine that Muscle Contraction is the result of Muscle 
Disintegration. — Manner in ichich ordinary Cohesion 
is brought into play. — Manner of Restoration. — He- 
rn oral of the Heat and Oxidized Bodies. 

Rigor Mortis. — Connection of Muscle for Locomotion. 
— Of Standing. — 'Walking. — Running. 

Animal motion is of two different kinds: 1st. It is 
accomplished by vibrating cilia ; 2d. By the contraction 
of cells arranged in the form of a fibre. 

OF CILIARY MOTION. 

The epithelial cells of the cylindrical and of the tessel- 
ated kind are occasionally arranged with delicate pro- 
jecting stria? on their free extremities. The length of 
these varies from the 3^ to the x \ of an inch. These 
strise are termed cilia, and the cells are said to be ciliated. 

Give examples of complementary or after-tastes? Of how many 
kin Js is animal motion ? Describe cilia and their movements. 




306 OF MUSCULAR MOTION. 

Examples are presented by the mucous membrane of the 
Fig. 99. respiratory surface and of the nasal 

cavities ; an illustration is given in 
Fig. 99. The cilia may be regarded 
as prolongations of the cell wall itself. 
They exhibit a vibratjng motion back 
and forth, recalling tKe movements of 
stalks of grain in a field as the wind is 
ciliated cells. passing over it, the ears bending down 
and rising again in the breeze, and throwing the whole 
surface into waves. The cilia also exhibit a movement 
like that known as the feathering of an oar, or sometimes 
as turning round upon the point of attachment, as upon 
a centre, giving rise to a sort of conical motion, the free 
end describing a circle. These motions seem to be per- 
fectly involuntary, for they not only take place long after 
death, but even in detached portions, the ciliary cell be- 
ing uninjured and entire. The seats of ciliary action are 
always moistened surfaces. 

Ciliary motion is independent of nervous agency. 
The control of temperature and of chemical reagents 
over it shows that it is q£ a physical nature. 

Of Muscular Motion. 

The muscular system consists of muscular fibres, ten- 
dons, bones, together with various accessory parts, such 
as ligaments, sheaths, bursae mucosae, synovial capsules, 
fascia. Its' action depends on the primary fact that, un- 
der appropriate influences, muscular fibre shortens. 

Each voluntary muscle consists of a collection of fas- 
ciculi, exhibiting the characteristic appearance of trans- 
verse striation, as in the photograph of muscular struc- 
ture of the frog {Fig. 100). The primary fasciculi are 
collected into larger bundles, secondary muscular fascic- 
uli, held together by connective tissue, and these, again, 
into still larger, the tertiary. 

The primitive fasciculus is enveloped in a delicate 
sheath, the sarcolemma, as shown in Fig. 101, in which 
the fasciculus, though torn across, is held together by 

How is ciliary motion known to be involuntary ? How is it known 
to be of a physical nature ? Of what does the muscular system con- 
sist ? What is a muscular fasciculus ? Into what larger bundles is 
it collected ? <*- 



MUSCULAB FASCICULI AND FIBRILS. 307 

100. 




Striated muscular fasciculi, magnified 125 diameters. 



Fig. 101. 




Human sarcolemma. 

Fly. 102. 



the sarcolemma. The 
specimen is from the 
human muscle. Fig. 
102 is a good represen- 
tation of the same fact. 
The sarcolemma is a 
delicate membrane, of 
great tenuity in man. 
Within the sarcolem- 
ma the primitive fas- 
ciculus is seen to be 
composed of many par- 
allel fibrils, which may, 
by maceration or chem- 
ical agents, be separa- BuwIamnaoffislL 
ted from one another. These fibrils present a beaded 
aspect, and, since their constituent elements are arranged 
side by side in parallel planes, they give to the fascicu- 
lus the appearance of striatum it presents. The longi- 
tudinal striation of the fasciculus arises from the fibrils 
themselves. 

JFtg. 103 fpr: is a photograph of ultimate mus- 

cular fibre of the pig. The rectangular form of the 




What is the sarcolemma? 
muscle fibre due to ? 



What is the appearance of striation in 



308 FORMS OF MUSCULAR FIBRE. 

Fuu 103. 




Ultimate muscular fibre, magnified 200 diameters. 

constituent cells is well seen at a a a. At 5, probably 
by reason of a twist, tension, or undue strain, a spiral 
appearance is presented ; c c are the primitive fasciculi. 
A fluid surrounds the fibres of striped muscles, and 
the fibre cells of smooth ones, which is wholly different 
from the plasma of the blood. It contains a large 
amount of casein. 

It is commonly stated that muscular motion is accom- 
plished by fibres of two different kinds : 1st. The simple, 
non-striated, unstriped, or organic fibre ; 2d. The stri- 
ated, striped, or voluntary fibre just described. Though 
this subdivision may be convenient, it can scarcely be 
regarded as accurate, since the former variety passes by 
insensible degrees during development into the latter, 
and cases, indeed, are not wanting in which the same 
fasciculus presents in different parts both conditions at 
once. 

The non-striated muscular fibre, Fig. 104, consists of 
translucent bands of a soft granular material, varying 
from the ^-^ott to ToVo of an inch in breadth, and exhib- 
iting here and there the traces of nuclei, particularly aft- 
er the fibre has been acted on by acetic acid, as is shown 
in Fig. 105. Each fibre may be regarded as an arrange- 
How many kinds of muscular fibre are there ? Why is not this di- 
vision strictly accurate ? Describe the non-striated muscular fibre. 



FORMS OF MUSCLE. 
Ftff. 104. 



309 




Unstriped fibres. 
Fig. 105. 




Fig. 106. 



£ 

e 



Unstriped fibres in acetic acid. 

raent of nucleated cells, the nucleus being of a cylindroid 
or spindle form. The contractile content within is syn- 
tonic Non-striated fibre is not usually attached to fix- 
ed points, as to bone, but, by being collected into par- 
allel bundles, different bundles interlacing with one an- 
other, contractile planes or surfaces are formed, such as 
the cylindrical coat of muscular structure of the digest- 
How may the nuclei of it be rendered apparent ? IIow is it usu- 
ally arranged ? 



310 STRUCTURE OF MUSCLE. 

ive tube, or the contractile layer of the urinary bladder. 
Similar fibres, imbedded in the skin and connective tis- 
sues, communicate to them the quality of corrugation or 
contractility. The fasciculi are bathed externally with 
an acid juice, characterized by containing salts of pot- 
ash, phosphoric acid, creatine, and inosite. The general 
appearance of fibre cells of this class is given in Fig. 
106 (page 309) : a is from the small intestine of man; 
b y from the fibrous investment of the spleen of the dog. 
The striated muscular fibre consists therefore of fas- 
ciculi, with an elastic investment of sarcolemma, collect- 
ed into bundles. The contractile constituent is syn- 
tonin ; and though the general rule is that the primitive 
bundles shall run isolatedly and parallel to each other, 
in certain cases they anastomose. In its ultimate con- 
struction, the form of fibre may be regarded as consist- 
ing of a series of cells, as shown in Fig. 103, the diam- 
eter of which varies according to the actual condition 
of the muscle, whether it is in the contracted or relaxed 
state, but it may be taken, on an average, at the i ooo 
of an inch. The cells are placed end to end, the bound- 
ary walls upon the end presenting the appearance of a 
delicate transverse line. In length, muscular fasciculi 
vary from the sixth of an inch to two feet. The larger 
animals furnish some that are even much longer. The 
normal form is doubtless cylindrical, but this is constant- 
ly departed from, each accommodating itself to the press- 
ure of the adjacent ones. The sarcolemma serves as a 
partition between its included fibrils and the capillary 
Fi 10T blood-vessels and nerves, 

which imbed themselves in 
the rounded angular spaces 
between adjacent bundles. 
The cross section of a portion 
of muscle shows the manner 
in which the sarcolemma and 
the fibres are arranged. Fig. 
107 is from the human biceps. 
It has already been stated, 

Transverse section of human muscle. . ,. ^ .,-, 7-7. -,~a 

in connection with Joig. 104, 
With what juice is it bathed? What is the contractile constitu- 
ent of striated fibre ? What is the diameter of its constituent cells ? 
Of what length may such fibres be ? How are the blood-vessels and 
nerves arranged ? 




STRUCTURE OF MUSCLE. 311 

that the striated form of muscular fibre derived its name 
from the circumstance that, when examined by a suffi- 
ciently high power, it appears to be crossed by delicate 
transverse lines, the longitudinal separations between 
the fibrils being also visible. This is seen in the speci- 
men of insect muscle represented in the photograph, 
Fig, 108, and under a still higher magnifying power in 

Fin. 108. 




Non-fibrillated insect fasciculi, magnified 50 diameters. 

that of Fig. 109. The distance between the transverse 

Fig. 109. 




Non-fibrillatcd tmect f.*i.-cicuii, magnified 200 diameters. 



stria* varies with the condition of the muscle, but on an 
average it is represented aa being about the p * 00 of an 

From what does striated muscle fibre derive its name? What Is 
the average distanee between its stria- ? 



312 



MANNER OF MUSCULAR CONTRACTION. 



inch. Many more striae are crowded together when con- 
traction takes place, and they retire from each other as 
soon as relaxation occurs. 

It is said that the voluntary muscles contain in their 
muscle juice more acid than is enough to neutralize all 
the alkali of the blood. The electro-chemical relations 
of this interfascicular acid juice and the alkaline plasma 
of the blood are doubtless the cause of the production 
of those electric currents which have been demonstrated 
in the muscles. It does not follow, therefore, that these 
currents occur in the natural state : they may be the re- 
sult of the experimental arrangement for their own de- 
tection, since it has long been known that an acid and 
an alkaline juice, separated from each other by a con- 
ducting organic body, will form an effective voltaic 
circle. 

The contraction of a muscular fibre does not take 
place throughout its whole length at once ; it generally 
begins at the end, a change of aspect arising from the 
approach of the opaque centres of the cells to one anoth- 
er, and this occurring simultaneously across the whole 
fibre. This approach may, however, ensue in different 
parts of the length at the same time, the sarcolemma 
being raised up in bullae as the contraction takes place. 

Fig. 110. 




Contracting muscle of Dytiscus. 




Fasciculus contracting. 



This effect is shown 
in Fig. 110, in which 
the thickened portion 
of the contracted mid- 
dle space of the mus- 
cle is surrounded with 
the sarcolemmic bul- 
lae. Fig. Ill exhibits, 



How may electric muscle currents be explained ? In what man- 
ner does the contraction of a muscle take place ? What happens to 
the sarcolemma? 



ATTACHMENT OF MUSCLE TO BONE. 313 

under the same circumstances, a fasciculus from the eel, 
a being the uncontracted, b the contracted part, on the 
edge of which the sarcolemma is again raised up. 

Different portions of the length of the fibre assume 
this condition at different moments, and hence the whole 
structure is thrown into a form recalling the motion of 
a worm. The zigzag appearance arises from thtj circum- 
stance that when relaxation of the fibre occurs all its 
parts are not brought at once into the same state, but 
while some are contracted others are in the opposite 
condition. It is to this reciprocation of motion that the 
sound usually emitted while the muscle is in action, a 
low ringing sound, is to be attributed. 

Striated muscle is often attached to bone, or other 
substance on which it has to exert its mechanical pow- 
er, by intervening fibrous tissue constituting tendon. 
These fibres are collected in groups, so as to present 
primary, secondary, and tertiary fasciculi. The tendin- 
ous fibres are brought in relation with the sarcolemma, 
and thus form a sheath connected with adjacent ones by 
other detached fibres. 

From the peculiar struc- Fin - 112j 

ture of muscular tissue, the 
capillary vessels distributed 
to it must run in a direction 
for the most part parallel to 
its fibres, as in Fig. 112. 

In the same general man- 
ner that the blood-vessels are 
distributed, so likewise are 

the nerves. An example Of Distribution of macular capillaries. 

this is Been in ////. l ] :',, p. 314. They never penetrate 
the sarcolemma, but run in close contiguity with it, their 
distribution to different parts of the fasciculi being very 
unequal. 

; BX I'T\< i Joy OF KT/84 ULAB FIBBB. 

The mechanical action of mtl8Calar fibre depends on 

all portion! of the length of a fibre in contraction at once? 

adjacent fibre* all simultaneously contracted ? What \t the 

the sound a muscle emits? What i- the mode ofattach- 

* of muscle to bone? In what manner i.s the distribution of 
blood-vc.-sd- and nerves to muscles arranj 

o 




314 



FUNCTION OF MUSCULAR FIBRE. 

Fig. 113. 




Distribution of muscular nerves. 

the shortening of the long axis of the cells of which the 
fibres are composed. To this result the designation of 
contractility is given. 

At one time it was supposed that the contraction of 
a muscular fibre depends so completely upon the agency 
of the nervous system that it might be considered as 
the direct function thereof; but a more critical examin- 
ation of the circumstances of the shortening of the fibre 
cells shows that it possesses many features in common 
with the same contraction of the cells of plants, which 
have no nervous system. The influence passing along 
the nerve fibrils is only one out of many capable of caus- 
ing muscular contraction. There is abundant evidence 
in support of the position that contractility is the result 
of the structure of the muscular fibre, and that it be- 
longs to it, and is not a special function of nerves. 

When muscular fibres are touched by a pointed in- 
strument, they exhibit contraction even after they have 
been detached from the body, provided that too long a 
period of time has not elapsed. If it be of the striated 
variety, the bundle that has been disturbed alone con- 
tracts, and presently after relaxes ; but there is no lat- 
eral spread or diffusion of the effect to adjacent bundles, 
except in the case of the heart, in which it would ap- 

What is meant by contractility? How is it known that contract- 
ility does not depend on the nerves? What occurs when striated 
fibre is touched by a pointed instrument ? 



CONTRACTION OF MUSCULAR FIBRE. 315 

pear that the contraction of one part is diffused lateral- 
ly, and a single disturbance is followed by many altern- 
ating contractions and relaxations, simulating, as it 
were, the normal function of the whole organ. But 
where the non-striated form is in like manner examined, 
the contraction takes place more slowly, spreads lat- 
erally to a wider extent, and is followed by a relaxa- 
tion. ' 

The capability of contracting continues in muscle 
fibre for a certain time after death, a period shorter as 
the rate of respiration is higher, and hence these effects 
were first observed by Galvani and others in the case 
of the frog and cold-blooded animals. Even after it has 
disappeared, it may be re-established by continuing the 
supply of arterial blood, as Dr. Brown-Sequard has 
shown : a fact illustrating in a striking manner the in- 
dependence of the muscular contraction of the nervous 
>v>tem. Of course, as would have been expected, what- 
ever interferes with due arterialization interferes with 
muscular power. This is the reason of the inability for 
exertion experienced in the thin air of mountain tops. 
The converse of this likewise holds good : the higher 
the rate of respiration, the more energetic the muscular 
power ; and therefore, in birds, which respire most per- 
fectly, muscular contractility is exhibited with the great- 
est energy. 

The immediate cause of muscular contraction is to be 
sought for in the muscles themselves. So far from there 
being any thing mysterious or incomprehensible about 
it, as some writers insist, we probably shall not be very 
far from the truth if we assert that muscular contraction 
is the necessary physical result of muscular disintegra- 

Reviewing the various conditions under which con- 
traction occur-, destructive metamorphosis is the pri- 
mary and leading one. Every thing seems to indicate 
'that the COBtaaction of a fibril can not take place with- 
out the loss of a part of its substance, and this ensues 

What occurs when the non-striated kind u used? In what dam 

of animals <! tility continue longest after death? Il<>w 

What effect have rarefied end condensed air <>n 

r-ontrafction ? What is the eanse of muscular contraction? Can a 

fibril contract without !< ht ? 



316 ACCUMULATION OF WASTED MATERIAL. 

even in the artificial motions that are established by- 
electric currents in amputated muscles. 

I therefore regard disintegration of the muscular 
structure as the primitive act, so far as the fibril itself is 
concerned, and contraction as the necessary consequence, 
that disintegration being brought about by the oxidiz- 
ing agency of arterial blood. It must, however, be 
borne in mind that this waste is masked by its incessant 
repair, and that its condition at any moment of its ac- 
tion represents the actual balancing at that instant of 
the waste and repair respectively ; and since the repair 
does not proceed with the same rapidity as the destruc- 
tion, it needs must follow that, sooner or later, a point 
will be arrived at when there is an absolute necessity 
for repose to give to the renovating processes the op- 
portunity or time for effecting a complete restoration. 

It is probable that one cause of cessation of muscular 
contraction in any one point of a fibre is the momentary 
accumulation of wasted material, as might be illustrated 
in a coarse manner by the difficulty of causing a fire to 
continue burning when the ashes are permitted to ac- 
cumulate, and the necessity of their removal before the 
combustion can go on. Two separate events have to 
occur before a fibril that has been in contraction is 
ready to contract again : these are the removal of the 
oxidized products, and the renovation of the interior of 
the cells. The two probably go on coincidently, the 
veins taking one part of the duty, and the arterial cap- 
illaries the other. 

In non-striated muscular fibre, in which the supply of 
blood-vessels is much less copious, there is a possibility 
for a lateral propagation of effect, because of the possi- 
bility of the lateral propagation of the heat, either sup- 
plied directly from the nerve tubule or arising from the 
oxidation going on. The sluggishness of its first con- 
traction, the longer continuance, the propagation from 
fibre to fibre laterally until the effect wears* out or is re- 
enforced by some new stimulus, might almost seem to 

In contraction what is the primitive act ? How is the disintegra- 
tion brought about ? How is it that the state of the muscle may be 
said to be masked ? What is probably the cause of the local cessa- 
tion of contraction ? What are the peculiarities of non-striafed fibre 
contraction ? 



CONTRACTION OF MUSCLE. 317 

be the necessary result of the imperfect supply of arte- 
rial blood, the sluggish removal of the products of waste, 
and the more perfect opportunity for the diffusion of 
heat. This doctrine therefore meets with a very happy 
illustration in the phenomenon displayed by the con- 
traction of the two kinds of fibre. 

But the question returns upon us. Admitting the 
descriptions that have now been given to be a true 
representation of the facts, and also of their natural 
sequence, what is the actual physical cause of the short- 
ening of the muscular fibril? 

It is capable of demonstration that muscular contrac- 
tion ensues as the direct consequence of destruction of 
muscular substance, and that a great linear extent of 
movement may be accomplished by the removal of an 
insignificant amount of substance. If 100,000 fibrils 
lost one third of their entire substance — a thing which, 
of course, could scarcely take place — the diminution of 
weight would only amount to a single grain. Our con- 
ception of this action may perhaps be rendered clearer 
by an illustration. If we had an iron thread of excess- 
ive tenuity, composed, for instance, of a single row of 
iron atoms set end to end, and could, by suitable pro- 
cesses, effect the removal, here and there, of atoms in 
the line, an instantaneous contraction would be the re- 
sult, the thread shortening in proportion to the number 
of atoms removed, but shortening with an energy com- 
mensurate with the cohesive force of the iron itself, and 
yet ready to return to its original length the moment 
that fresh iron atoms present themselves to be intro- 
duced in the place of the abstracted ones; and so with 
muscular fibre, the molecular force of cohesion devel- 
1 here and there by the removal of tissue is to be 
measured only by the cohesion of the fibre, though the 

Ifl of material which may have been the cause of that 
force coming into play may be very small indeed ; nor 

- the quickness of relaxation present any difficulty 
when we consider the rapidity with which interstitial 
nutrition takes place, and the small quantity of matter 
to be supplied. 

peculiarities accounted for? What fa the physical 
m of the shortening of muscular fibril? How may this eneel l>c 

illustrate! ? 



318 



VOLUME OF CONTRACTING MUSCLE. 



Fig. 114. 



I can not at this point avoid offering a criticism on the 
experiments by which it has been attempted to prove 
that a muscle, when it contracts, loses none of its bulk ; 
the loss that does in reality occur is, it is true, very mi- 
nute, perhaps »o minute that, in the coarse apparatus re- 
sorted to in these experiments, it would be altogether 
inappreciable. Such a contrivance is rep- 
resented in Fig. 114, in which a a is a 
wide tube for containing the muscle, g; it 
is also to be filled with water, and from its 
side a narrow tube, J, projects, the water 
reaching to some such point as e. The 
tube, a a, being closed at both its extremi- 
ties water-tight by means of corks, b c, 
whenever the muscle is made to contract 
by an electric current, applied by means 
of the spring wires, f f, or otherwise, if 
enlargement occurred the water would rise 
at e, and if diminution it would descend ; 
but as, upon trial, it is found that no move- 
ment whatever takes place, it has been in- 
ferred that the volume of the muscle re- 
mains unchanged. But no compensation 
whatever for temperature is provided ! 
Yet it is positively known that w T hen a 
>t _ muscle contracts it becomes warm, and, 
ing muscle. doubtless, these instruments, if delicate 
enough, would have led to the preposterous conclusion 
that a muscle after contraction is larger than it was be- 
fore. But, even setting disturbances of temperature 
aside, such experiments are of no kind of value, since 
they contain no provision for the removal of the w T asted 
material of the muscle, which still continues a part there- 
of, though it has become, to all intents and purposes, ex- 
traneous, and would, if in the living system, have been 
instantly removed by the veins. 

Connected with the foregoing phenomena is that gen- 
eral rigidity of the muscles which occurs a certain time 
after death, and hence known as rigor mortis. This 
usually commences in the lower jaw and neck, invading 

Describe the experiment illustrated in Fig. 114. What obvious 
objections is it liable to ? What is meant by the rigor mortis ? In 
what order are the muscles usually affected by it ? 




Volume of contract- 



THE CONDITION OF STANDING. 319 

next the upper extremities, and reaching eventually the 
lower ones. After continuing for a period longer in pro- 
portion to the lateness of its beginning, relaxation ensues, 
the parts being affected in the same order as they were 
made rigid. The rigor mortis sometimes begins as soon 
as ten minutes after death, sometimes it is postponed as 
long as seven hours. In those who have died of chronic 
diseases it occurs and ceases very quickly. Both classes 
of muscles, striped and unstriped, are effected by it, and 
when it is over they present an unresisting and lax con- 
dition, and putrefactive change presently sets in. Even 
after cadaveric rigidity has been assumed, the contractile 
power gf muscles may be restored by furnishing them, 
through a suitable arrangement, arterial blood ; for this 
feet we are indebted to Dr. Brow r n-Sequard, his experi- 
ments having been made both upon man and animals. 
The arterial blood employed assumed, during its passage 
through the limb which was the subject of the trial, the 
venous character, and issued of a dark color. This res- 
toration of contractility was by no means imperfect or 
transient; in one instance it continued for two hours. 

By means of tendon the muscles are attached to the 
skeleton, which constitutes the solid framework of the 
system. Operating thus through the skeleton, the mus- 
cles are enabled to keep the entire body in the erect or 
standing position, and also to give it locomotion. 

In man, the power of standing implies the conservation 
of the line of direction of the whole body within the nar- 
row basis covered by the feet and between them. The 
head is balanced on the atlas so nearly under its centre 
of gravity that no ligamentum nuchae is required, as in 
the case of other animals, to prevent it from falling for- 
ward. Nevertheless, a forward motion can be executed, 
amounting to about 75 degrees from the perpendicular, 
and a lateral motion right and left of from 45 to 50 de- 
grees. In standing, the weight of the entire body is 
transmitted perpendicularly to the feet. These rest on 
the heel and the fore ends of the metatarsal bones, es- 
'ally of the great and little toes, and on the points of 
the The general centre of gravity of the entire 

body is a little above the transverse axis connecting the 

what artificial process may rigor mortis he counteracted ? De- 
scribe the condition of standing. 



320 MOVEMENTS IN THE ACT OF WALKING. 

heads of the thigh bones, and for equilibrium to be main- 
tained, a perpendicular line drawn from this centre must 
always fall within the basis inclosed by the contour of 
the feet. 

Even in the most perfect condition of rest that we can 
assume while maintaining the standing position, a great 
many separate muscular acts are necessarily required. 
Apart from those little voluntary changes incessantly 
occurring, the rhythmic action of the muscles involved 
in respiration, especially those of the abdominal walls, 
is perpetually changing the position of the centre of 
gravity, and therefore those muscles employed in keep- 
ing the spine erect are obliged to assume an antagoniz- 
ing rhythmic action. This is at once the reason of the 
fatigue we experience in long standing, and of the diffi- 
culty infants encounter in their attempts to maintain the 
erect position. 

In walking, the legs act like a pair of pendulums. The 
head of the thigh bone, which is their centre of motion, 
is held in its socket, not by muscular exertion, nor by its 
ligamentous arrangements, but by the pressure of the 
air, a fact that may be proved by very simple experi- 
ments. If the pressure of the air be removed, as in an 
exhausted receiver, spontaneous dislocation ensues. The 
trunk of the body is like a rod balanced on an axis pass- 
ing through the hip joints, and advancing with the move- 
ment of the legs like a rod balanced on the tip of the fin- 
ger. It is inclined forward or backward in correspond- 
ence with the motion or with the resistance of the wind ; 
if the wind blows in front, we lean forward ; if behind, 
we lean backward ; the angle of inclination being in pro- 
portion to its force. In walking there are two distinct 
periods : the body is first poised on one of the limbs, and 
then rests for a moment on both. The advancing limb 
swings like a pendulum, bending at the knee so as to be 
shortened one ninth ; the other straightening at the knee 
and hip joint, and so pushing the pelvis and trunk for- 
ward to be received on the limb that has just advanced. 
It is only in slow walking that the whole arc of motion 
is swung through, the time occupied being two thirds 

What is the cause of the fatigue experienced ? How is the head 
of the thigh bone held in its socket? What are the movements in 
the act of walking ? 



THE VOICE. 321 

of a second. In quick walking and running only half a 
vibration is accomplished, and this in half a second of 
time. In slow walking each foot rests upon the ground 
one third of a second. The longest step made is half the 
entire span of the two extremities. . To prevent swaying 
from side to side, the arms swing with the legs. 

In running there is a moment when both feet are off 
the ground at once, and the body actually projected into 
the air. In walking there is a moment when both feet 
are on the ground together, the one not being raised till 
the other is planted. In running the steps are, on an 
average, twice as long as in walking; and the number 
of steps made in a given time in running and walking 
respectively is as 3 to 2. 



CHAPTER XXI. 

OF THE VOICE. 

Origin of the Voice. — Comparative Physiology of 
yoise, Song, Voice. — Distinction beticeen Song and 
Speech. — The Larynx, and its Action in Singing. — 
Speaking Animals and Machines. 

For the production of the sounds necessary for inter- 
communication among the higher animals, and particu- 
larly for the speech of man, it might be supposed that 
some complicated and elaborate contrivance must needs 
be resorted to. This object is, however, accomplished 
by merely employing, on its escape from the system, the 
wasted product of respiration, the breath, which, as it 
ies outward through the respiratory passages, sets in 
motion a simple mechanism, and thereby originates all 
the exquisite modulations of song, and all the impress- 
ive utterances of speech. Is it not admirable that thus, 
out of dead and dismissed matter, results of so high an 
order, materially and mentally, arc obtained? 

What might be termed the comparative physiology 
of the voice is very simple. It appears first in inverte- 
brate animals as a monotonous noise or cry, which grad- 
ually, in higher tribes, becomes more varied in loudness 

AVhat are those in the act of running ? From what does the voice 
arise? Describe tlic comparative physiology of the voice. 

O 2 



322 SOUNDS PRODUCED BY INSECTS. 

and note. In the different stages of his existence man 
himself furnishes an illustration of this course. Voice- 
less before birth, with a piteous or monotonous cry in 
early infancy, articulate speech and song are the result 
of education, and through these the power is eventually 
gained of expressing the most refined emotions and the 
most elevated ideas. The solitary bell-like sound which 
the nudibr^nchiate gasteropods emit, thus produces, by 
its successive improvements, a wonderful result at last. 
Among insects the modes of producing sounds are 
very various, some effecting it by percussion, some by 
the friction of horny organs. In others, the extremity 
of the trachea, through which the air escapes, is accom- 
modated with vibrating membranes. The contractions 
of the muscles of the wings, brought vigorously into ac- 
tion during flying, occasion an alternate pressure and re- 
laxation upon the tracheal tubes. The air, thus passing 
in and out, throws into vibration the valves of the spir- 
acle, which, as seen in Fig. 115, are suspended upon a 

Fig. 115. 




Spiracle of insect. 

dozen or more flexible supports ; but their free edges, 
approaching within a certain distance of each other, are 
thrown into quick vibration by the passing current, in 
the same manner as is the vibrating spring of the ac- 
cordeon. These vibrating plates of insects are the ru- 
How are sounds produced by insects? Describe Fig. 115. 



RUDIMENTARY SOUNDS. 323 

diments of the perfect vocal apparatus in man. Again, 
in others, the swiftly-recurring beating of the wings pro- 
duces a sound, as, for example, in the musquito. Among 
vertebrated animals, those that breathe the air are vo- 
cal, nearly all fishes being mute. From fishes, as we 
pass upward, the sound and the instrument making it 
increase together in complexity. Through a simple 
chink, the air expelled from the respiratory sacs of 
snakes, by the contraction of their abdominal muscles, 
issues forth as a mere hiss, the sound being increased in 
the frog by the development of resonant cavities. From 
such simple noises we are conducted to the musical 
notes of birds, some of them being of exquisite purity 
and sweetness. In these, the vocal glottis is situated at 
the bifurcation of the trachea, another glottis being 
above for the final escape of the air. These vertebrated 
animals first introduce us to the mechanism for articu- 
late speech, the raven and parrot being able to pro- 
nounce words with distinctness. The articulation is ef- 
fected, as in man, by the motions of the tongue and oth- 
er portions of the mouth. 

For the farther consideration of this subject, it is nec- 
essary to understand that there is a distinction between 
song and speech. Song is produced by the glottis, 
speech by the mouth ; or, perhaps, a more correct state- 
ment would be, that the larynx is the organ of song, the 
mouth of that form of speech called whispering, and for 
which nothing is required but a stream of air issuing 
from the fauces, the tongue and other organs giving it 
articulation ; but for audible speech, a noise is created 
in the larynx, and modified by articulation in the mouth. 

The double larynx of birds is replaced by a single lar- 
ynx in man, serving at the same time for the entrance 
and exit of air, and likewise for vocalization. Birds 
having no lower larynx are voiceless. A general idea 
of the construction of the organ of voice in man maybe 
gathered by supposing it to be composed of three por- 
tions, the trachea, the larynx, and the mouth. The tra- 
chea is the tube by which air is brought from the lungs 

How arc sounds produced by reptiles? Now are articulate sounds 
produced by certain birds? In wbat manner are speech and song 
respectively produced ? What is the construction of the human lar- 
ynx? 



324 ACTION OF THE VOCAL CORDS. 

and delivered into the larynx, a superposed structure, 
arranged upon the cricoid cartilage, on which is articu- 
lated the thyroid cartilage by its lower horns, around 
which a certain degree of rotation can be accomplished, 
so that the front of the thyroid may be elevated or de- 
pressed with a kind of bowing motion. Posteriorly, on 
the cricoid cartilage are placed the arytenoid cartilages, 
which can be approached or separated from each other, 
and from their summits pass to the front of the thyroid 
cartilage the inferior laryngeal ligaments or vocal cords. 
These constitute the essential organ of sound. The thy- 
roid cartilage, by its motions, can determine the strain 
put upon them, and the arytenoids can either bring them 
into parallelism, or place them at an acute angle. The 
chink or fissure between them is the rima glottidis : its 
figure and width vary with the recession or approxima- 
tion of the vocal cords, which, as the air passes by them, 
are thrown into vibration in the same manner as the 
reed in musical instruments. The epiglottis cartilage, 
which is above, guards the passage, and may also be 
supposed, by its descent, to deaden the sounds. 

The slowness or rapidity of the vibration is dependent 
on the stretch of the vocal cords. The manner in which 
various degrees of tension can be given to the cords is 
readily understood by considering their attachments. 
In front, as we have said, they are fastened to the thy- 
roid cartilage, posteriorly to the arytenoids. When the 
thyroid cartilage executes a bowing motion forward, 
the vocal cords are put upon the stretch, and similar va- 
riations of their tension and also of their position can be 
given by the movements of the arytenoid cartilages be- 
hind. When the air is moving in and out without giv- 
ing rise to any sound, the chink of the glottis is angu- 
lar, its point being forward, and from that the cords di- 
verge posteriorly. For the production of sound, the 
cords must be brought parallel, or even inclining toward 
each other. If they incline away from each other, no 
sound will be produced. The pitch of the note will be 
determined by the stretch of the cords, and this, in its 
turn, will be determined by the contraction of the vocal 
muscles. The crico-thyroid and stern o-thyr oid bow the 

How are the vocal cords regulated? In what position must the 
cords be to produce sound ? 



THE LAKY XX. 



325 



Fig. 116. 




front of the thyroid cartilage down, the thyroarytenoid 
and thyro-hyoid carry it back; the former therefore 
stretch the cords, and the latter relax them. The open- 
ing of the glottis is likewise determined by other mus- 
cles, the posterior crico- arytenoid dilating it, and the 
lateral crico-aryteuoid and the transverse arytenoid clos- 
ing it. 

II (j. 116 is the larynx, seen in profile: 
a a, hall' oi the hyoid bone ; 6, thyroid car- 
tilage, cut; c, thyro-hyoid membrane; c?, 
cricoid cartilage ; e, trachea ; jf, oesopha- 
gus ; 7, epiglottis ; />, great horn of the thy- 
roid cartilage, united to ?, the great horn 
of the os hyoides, by A", the lateral thyro- 
hyoid ligament; /, thyro-hyoid membrane, 
traversed by the superior laryngeal nerve; 
?/?, posterior crico-arytenoid muscle; ??, lat- 
eral crico -arytenoid; 1, inferior laryngeal 
nerve ; 2, posterior crico-arytenoid twigs ; 
3, lateral crico-arytenoid twigs ; 4, thy ro-ary tenoid twigs ; 
5, arytenoid twig. 

Fig. 117 is the posterior view of the 
larynx : a, base of the tongue; 5, poste- 
rior border of the thyroid cartilage; c c, 
thyroid body; cZ, posterior crico-aryte- 
noid muscle ; e, arytenoid muscle ; 11, 
superior laryngeal, traversing the supe- 
rior thyro-hyoid membrane, and giving 
off lingual and epiglottic branches, and 
others to the mucous membrane cover- 
ing the posterior face of the larynx; 2, 
twig for the arytenoid muscle; 3, anas- 
tomotic of Galien ; 4, inferior laryngeal ; 
5, tracheal branches ; C, twig for the pos- 
terior crico-arytenoid muscle; 7, twig for the arytenoid 
muscle; 8, branch for the lateral crico-arytenoid and 
rioi crico-arytenoid muscles. 

The larynx is essentially a reed instrument with a 
double membranous tongue. That the rima glottidifl ifl 
the seat of the origin of the sound is proved by the fact 

Desn . ll<), 117. To what class of instruments does tli", 

larynx belong? How may it be proved that the lima glottidifl ifl the 

seat of sound ? 



Profile of larynx. 



Fig. 117. 




Posterior view of 
larynx. 



326 SPEAKING MACHINES AND ANIMALS. 

that when an aperture exists in the trachea below the 
glottis the voice disappears, but if above the glottis there 
is no effect. Moreover, the human or animal larynx can 
be made to produce its characteristic sounds with more 
or less distinctness, after it has been removed from the 
body, by directing a current of air through the trachea. 
Cases have occurred which have afforded the opportu- 
nity of observing the condition of the glottis while emit- 
ting sounds. The vocal cords are brought into parallel- 
ism with one another, and separated by an interval of 
scarcely more than from the -^ to the -^ of an inch ; 
but when the air is moving in and out silently, the fis- 
sure assumes a divergent or triangular form. 

An artificial larynx will give rise to sounds analogous 
to those of the human larynx. Such have been made 
of leather, and, better still, of caoutchouc. 

The narrower the glottis is made, and the more tight- 
ly the cords are strained, the more rapidly they will vi- 
brate, and the higher will be the musical note emitted. 
In an individual the range of the voice is rarely three 
octaves, but the male and female voice, taken together, 
may be considered as reaching to four. Generally, the 
lowest female note is about an octave higher than the 
lowest male, a similar remark applying to their highest 
notes respectively. 

While thus song is laryngeal, speech, which is a modi- 
fication thereof, is oral, or produced by the mouth. Man 
is not alone endowed with the faculty of uttering artic- 
ulate sounds : several other animals, by education, may 
be taught to express them. Ingenious mechanics have 
also repeatedly invented speaking instruments, upon the 
same principle as that of the vocal organs, of combining 
the sounds of letters into words, and even into sentences, 
a convincing proof not only of the mechanical nature of 
articulate sounds, but also of the perfect manner in which 
the natural mechanism is understood. Animals which 
have been taught to speak may also be regarded as au- 
tomata, for they have no comprehension of what it is 
they are uttering, and never produce articulate combina- 
tions spontaneously, but only as the result of instruction. 

How near are the vocal cords to each other in the act of producing 
sound ? What is the effect of narrowing the glottis ? What is the 
range of the male and female voice? On what principle have speak- 
ing machines been made? 



OF THE ORGANIC CELL. 327 



CHAPTER XXII. 

OF THE ORGANIC CELL : ITS DEVELOPMENT AND 
REPRODUCTION. 

Simple and Nucleated Cells. — The Simple Cell: its 
Parts and Functions. — The Nucleated Cell: its 
Parts and Functions. — Activity of the Nucleus. — 
Other Forms of Cells. — Cells arise by Self -origina- 
tion and Reproduction, — Reproduction by Subdivi- 
sion, Budding, and Endogenously. 

The Animal Cell. — Forms of Cellular Tissue. — Forms 
of Vascular Tissue. 

The organic cell, the starting-point of every organ- 
ism, vegetable or animal, consists of a vesicle or shell, 
with included contents. If the vesicle be of uniform 
thickness all over, the cell is a simple one; but if there 
be upon some portion of it a thickened granular spot, 
the cell is said to be nucleated. 

The vesicle of the simple vegetable cell, more close- 
ly examined, is found to be composed of different lamina? 
or strata. The innermost, designated the primordial utri- 
cle, consists of an azotized substance, a member of the 
protein group. On the exterior of this pellicle, and, as 
it were, arising from its surface, lies the cell wall, serv- 
ing to give protection to the parts within. 

Within the primordial utricle, the cell contents pre- 
sent themselves of a different nature and different form, 
according as the species of the cell may be. In differ- 
ent hey are colored of various tints, and are of 
various consistency, more solid or more liquid. To the 
cell-contents the convenient designation of endochrome 

Jven. This interior content is not to be understood 
as having a homogeneous constitution, since sometimes 
even its colored portions are separated out and arranged 
in dots or spiral lines, very distinct from the remaining 
onoolored mat. -rial. 

What i- tli'> difference between a simple and a nucleated cell? 
Of what parts ia the limple Yegetable cell eonpoeed? What is the 
endochrome ? 



328 SUBOKDINATE FORMS OF CELLS. 

The active portion of such a cell consists of the utricle 
and endochrome conjointly, the cell wall only discharg- 
ing a mechanical office. In the simple cell, all parts of 
the utricle appear to be endowed with equal power for 
carrying on the functions of the organism. 

But in those cells possessing a nucleus, the energy is 
no longer diffused with uniformity, the nucleus concen- 
trating much of the power in itself, and serving as a 
centre of activity. 

There are subordinate species of cells, as the spiral and 
the dotted. These exhibit points of re-enforcement or 
thickening, such as the appearance of a thread wound 
spirally, or in dots here and there on the interior of the 
wall. There would seem to be a tendency during the 
development of a cell for these parts to assume a spiral 
arrangement. 

Thus constituted, each cell runs through a definite cy- 
cle or career, having its moment of birth, its period of 
maturity, its time of death. During its mature life it 
discharges with activity the special function to which it 
is devoted, but in so doing becomes eventually worn out 
and old. The period of activity of cells of different spe- 
cies is very different, some passing away quickly, and 
others having a longer duration. 

The commencement of cells is either, 1st, by self-orig- 
ination, or, 2d, by reproduction. 1st. Cells arise in an ob- 
scure manner from homogeneous particles floating in a 
protoplasma, which, taking on development, have a ves- 
icle thrown over them, and, being of a spherical shape, 
present the aspect of a cell wall and cavity. The granu- 
ular content by degrees increases as the young cell grows 
in all its dimensions. From that granular content new 
cells may arise. 

2d. Cells are reproduced from antecedent ones of the 
same kind by subdivision, by budding, by endogenous 
generation. 

The reproduction of cells by subdivision is strikingly 
illustrated by the Hsematococcus binalis. The manner 
of the process seems to be as follows. The endochrome 
of the original spherical cell, a, Fig. 118, begins to un- 

Of what does the active portion of the vegetable cell consist ? What 
other subordinate forms of cells are there ? In what modes do cells 
originate ? What is meant by self-origination ? What by subdivision ? 



ENDOGENOUS GENERATION. 



329 




Reproduction of Haematococcus binalis. 



dergo bi-partition as at ft, 

and as the dividing portions 
recede from one another 
the primordial utricle bends 
round them. Next a layer 
of permanent cell Avail, of a 
mucous character on its ex- 
terior, is produced, which 
accompanies the inflection 
of the primordial utricle as 
at c, and, after a while, the 
bi-partition is complete, and 
the separated portions con- 
stitute distinct individual 
cells. The subdivision may 
be repeated as at d. 

The cells that have thus arisen by subdivision soon 
grow to the size of the one from which they were de- 
rived, and are ready for subdivision in their turn. In- 
deed, it often happens that traces of incipient subdivision 
may be detected long before the cell has reached its ma- 
ture dimensions. 

The reproduction of cells by budding may be illus- 
trated by the vesicles of the yeast-plant; and though, in 
those cases in which the budding cell possesses a nucle- 
us, the nucleus is not necessarily involved. 

Cells are said to arise from endogenous generation 
when they make their first appearance in the cavity of a 
former cell, of which the endochrome exhibits a disposi- 
tion to divide into many small portions, at first doubt- 
fully, then more distinctly, and each one of these por- 
tions obtaining a covering investiture or primordial 
utricle for itself. The process continues until the young 
brood of cells has reached a certain degree of perfection, 
when they escape from their confinement, either by the 
Gssnring or deliquescence of the old cell wall. 

The animal cell presents a structural arrangement 
differing from the vegetable in this, that it does not pos- 

ss a proper cell wall, but consists of a primordial utri- 
cle and interior content alone. Its manner of reproduc- 

What illustration is there of cell-reproduction by budding ? What 
is meant by endogenous generation? In what respect docs the ani- 
mal cell differ from the vegetable? 



330 



CELLULAR TISSUE. 



tion is of three kinds : 1st. From germs ; 2d. By fissure ; 
3d. Endogenously. Where animal cells originate from 
germs, these seem to be granules of a substance analo- 
gous to fibrin, floating in the formative liquid. In du- 
plication by subdivision, the import of the nucleus is 
shown by the fact that the action begins at it. It may 
be said of animal cells that the nucleus maintains a more 
conspicuous relation than it does in the case of vegeta- 
ble ones. Reproduction in the endogenous manner is 
carried forward in the case of these cells in the manner 
described in a preceding paragraph. 

OF THE CONSTRUCTION OF CELLULAR AND VASCULAR 

TISSUES. 

By their development and juxtaposition with one an- 
other, cells give rise to continuous fabrics of various 

, kinds, or cellular tissue. 

If the development of 
new cells occurs in a 
space where there is 
freedom from pressure, 
the cells maintain their 
original spherical form, 
as seen in the photo- 
graph, Fig. 119. But 
should the develop- 
ment occur in a con- 
fined space, or under 
circumstances of pres- 
sure, the intercellular 
spaces necessarily ex- 
isting in the former case 

Simple cellular tissue, magnified 50 diameters. ., & „ . , 

by reason of the spher- 
ical shape, are now encroached upon, and the cells assume 
various angular forms, such as paraHelopipedons, rhom- 
bic dodecahedrons, etc. Of the former we have an ex- 
ample in the photograph, Fig. 120, representing a sec- 
tion of muriform cellular tissue. In other cases, with a 
view of giving resistance to pressure, the interior of 
each of the cells is fortified by a fibre, and thus arises 

In what three ways may it be reproduced ? How does cellular tis- 
sue arise ? Under what circumstances do developing cells change 
their form ? 




CELLULAR TISSUE. 



331 



the tissue of which we 
have an example in 
the photograph, Fig, 

121. Tw# or more fi- 
bres may in this man- 
ner be employed, and 
when Bach is the case, 

it is observed that 
they do not cross one 
another, the one wind- 
ing from right to left, 
the other from left to 
right, but they are 
laid parallel to each 
other, and form a 
compound strand. In 
other cases the con- 



Fin. 1*20. 




Muriforra cellular tissue, magnified 50 diameters. 
Fig. 121. 




Fibre-cellular tissue, magnified 50 diameter?. 

stituent cells of the tissue assume much more compli- 
cated forms, as, for instance, in the stellate variety. 
These more complicated forms prove that it is not alto- 
ber through the influence of a force of compression 
that cells assume modified shapes, but that on many oc- 
dons the disposition of their primordial utricle to 
branch in various directions is the true cause of the va- 
riation-. 

AN'hat is fibro-cellular tissue? 



332 



VASCULAR TISSUE. 



This disposition to grow spontaneously in one direc- 
tion rather than in another is the cause of the produc- 
tion of the different kinds of vascular tissue. A cell un- 
dergoing extreme elongation in one direction* either by 
reason of this quality of its primordial utricle, or through 
unequal nutrition, or other cause, gives origin to a tube. 
And if, of several cells thus elongated, and placed end 
to end on each other, the terminal portions should be 
obliterated either by rupture or absorption, a vessel per- 
meable throughout is the result. In this manner vas- 
cular tissue arises. These vessels still exhibit the struc- 
tural peculiarity of the cells from which they have orig- 
inated in this, that they may be fortified in their interior 
with fibres wound in a spiral, and so constituting a spi- 
ral vessel ; or wound in rings, and forming annular ducts. 
Fin. 122. In like manner, through 

similar modifications, 
the varieties known as 
reticulated and dotted 
ducts arise. In these 
fibro-vascular tissues it 
frequently happens that 
the fortifying thread is 
double or even quad- 
ruple. Of spiral vessels 
derived from a cactus 
we have an example in 
the photograph, Fig. 
122, and in those from 
the banana in that of 

Spiral vessels of cactus, magnified 50 diameters. JTi(i 123. 

The spiral vessels of plants contain air. Other tubes 
are for the conveyance of liquid ; the laticiferous ves- 
sels, for example, which are branching tubes for trans- 
mitting the latex of plants. Again, in other cases, the 
interior of the vessel is more or less completely filled up 
by a gradual deposit of solid material, it being in this 
manner that proper woody fibre is formed from long, 
spindle-shaped cells. Vascular tissue in coniferous plants 
presents a peculiar dotted aspect from disc-like forms, 
exhibiting a pair of concentric circles, which are set at 

How does vascular tissue arise? What are spiral vessels? What 
are reticulated and dotted ducts? What is represented in Fig. 124 ? 




ANIMAL VASCULAR TISSUE. 

F?(j. 123. 



333 




Spiral vessels of banana, magnified 50 diameters. 

regular intervals upon it, as shown in the photograph, 
Fig. 124, which is clotted woody fibre from pine. The 

Fig. 124. 




Woody fibre of pine, magnified 50 diameters. 

Circular discs or glands run in single rows except in one 
place, where a double row is seen. Among true living 
pines more than two rows arc not met with. 

Animal vascular tissue arises in the same manner as 
vegetable, by the conjunction of elongated cells and the 

How does animal vascular tissue arise? 



334 



YELLOW AND WHITE FIBROUS TISSUE. 




obliteration of their r terminations. The physiological 
purposes these vessels subserve are, as in the other in- 
stance, the conveyance of gases or liquids. But fibres 
may form in animal fabrics without the previous inter- 
Fi 12g medium of cells, either 

directly from fibrin, the 
parts of which possess 
the quality of agglutin- 
ating into threads, or 
from the coalescence 
under like circumstan- 
ces of substances allied 
to gelatin, which yield 
the varieties of fibrous 
tissue known respect- 
ively as the yellow and 
the white, the former 
being composed of 
branching filaments, as 
seen in Fig. 125. It is 

Yellow fibrous tissue, magnified 300 diameters. ji i 

unacted upon by warm 
acetic acid, and, from its extraordinary elasticity, is used 
126 wherever that quality 

is required. The lat- 
ter, represented in Fig. 
126, shows strands of 
a wavy appearance : it 
is inelastic, softens un- 
der the action of acetic 
acid, being thereby dis- 
tinguished from the 
preceding, and is em- 
ployed on account of 
its tenacity wherever 
resistance to extension 
is required, as, for ex- 
ample, in the ligaments 
of the joints. The sol- 
id animal fibres are 
therefore employed where physical qualities are neces- 
sary, the hollow tubes for organic processes. By some 




White fibrous tissue, magnified 300 diameters. 



What is the difference between yellow and white fibrous tissue ? 



AREOLAR OR CONNECTIVE TISSUE. 



335 



physiologists it is believed that both yellow and white 
fibrous tissue arise from cells. 

Areolar or connect- TT . «„ 

t- -i ->- • Fig. 127. 

ive tissue, Jfiff, 127, is 

composed of the two 
preceding elements, the 
yellow and white fi- 
brous, interwoven with 
each other so as to con- 
st it ute a porous struc- 
ture, with a multitude 
of intercommunicating 
spaces. It is to be un- 
derstood that these in- 
terstices are wholly dis- 
tinct from cells ; hence 
the inapplicability of 
the term cellular, some- 
times employed for this 
tissue. Areolar tissue is employed for uniting the va- 
rious animal parts. Its interspaces are filled with a 
fluid, which, when in excess, is spoken of as dropsical 
effusion. Air, artificially or accidentally introduced at 
any point into it, may pass to every part, as is illustrated 
in cases of emphysema. The specimen from which the 
figure is taken was in this manner inflated. 

What is areolar tissue? In what respect does it differ from cel- 
lular tissue ? 




Areolar tissue, magnified 25 diameters. 



336 THE SPERM-CELL. 



CHAPTER XXIII. 
OF REPRODUCTION AND DEVELOPMENT. 

Reproduction: Conjugation. — The Sperm-cell: its Pro- 
duction. — Spermatozoa. — The Germ-cell: its Produc- 
tion. 

Ovum in the Ovary. — Its Structure. — Corpus Luteum. 

Ovum in the Oviduct. — Mulberry Mass. — Germinal 
Membrane. — The Chorion. 

Ovum in the Uterus. — Membrana Decidua. — Placenta. 
— Development of the Embryo. — Law of Von Par. 
— Types of Nutrition. — Of Conception. — Of Gesta- 
tion.— Of Parturition. — Influence of both Parents. 

In reproduction of the higher type two cells are nec- 
essary. These, differing in construction and also in func- 
tion, are designated the sperm -cell and germ -cell re- 
spectively. 

1st. Of the Sperm-cell. — The testes are the organs in 
which the sperm-cells arise in man. They are of an 
ovoid form ; each is covered with a white envelope, the 
tunica albuginea. A serous membrane, folded as a shut 
sac, overlies this tunic. From the inner surface a num- 
ber of delicate projections arise, dividing the organ 
into several compartments. In these compartments are 
lodged lobules arising from the tubuli seminiferi and 
their supplying blood-vessels. There are about 450 lob- 
ules in each testis ; their shape is conical, the diameter 
of the tubes of which they are composed about the -^J-g- 
of an inch. The total length of this tubular structure 
is about three quarters of a mile. Before the tubuli of 
each lobule reach the rete testis, they cease to be con- 
voluted, and bundles of them, uniting into larger ves- 
sels, are designated tubuli recti. In the rete testis there 
are from half a dozen to a dozen of these tubes, various- 
ly anastomosing with one another and dividing. They 

What cells are necessary in the higher development ? By what 
organs are the sperm-cells formed? Describe the parts of the testis. 
What is the length of its tubular structure ? 



THE TESTIS. 



337 



empty into the vasa efferentia, which, from being straight, 
become convoluted, a series of cones arising, together 
forming the globus major of the epididymis. This is a 
convoluted canal of about twenty feet in length ; de- 
scending, it receives beyond its globus minor the vascu- 
lum aberrans. It then empties into the vas deferens. 

Fig. 128, human testis: «, testis; £, lobes; c, tubuli 
recti ; (7, rete vasculosum ; e, vasa efferentia ; f, coni vas- 
culosi ; </, epididymis ; /*, vas deferens ; e, vas aberrans ; 
//*, branches of the spermatica interna of the testis and 

Fig. 128. 




The t 

epididymis; n, ramification on the testis; o, arteria de- 
ferentialis ; p 9 anastomosis with a branch of the sper- 
matic. 

The Becretion of the testis must betaken for examina- 
tion from the vas deferens or epididymis, before it has 

en mixed with the flnid of the prostate and Cowper's 

Describe Fvj. 128. 
P 



338 THE GERM-CELL. 

glands, or with mucus. It may be mingled with a little 
albumen or serum for the purpose of dilution, and, when 
examined with a power of 500 diameters, exhibits mul- 
titudes of moving bodies. These are the seminal ani- 
malcules, or spermatozoa. 

The spermatozoa are found in the spermatic fluid of 
all animals after puberty, their form being different in 
different species. Generally they may be described as 
consisting of a little oval-shaped head, from which a del- 
icate filament or tail projects. 

The motion of the spermatozoa is accomplished by 
means of their filament. It takes place in different ways, 
sometimes the filament vibrating like a whip, sometimes 
rotating like a screw, and sometimes a spinning round, 
as it were, upon a pivot, occurs, the filament having 
been coiled like a watch-spring. The rate of motion 
seems under the microscope to be rapid ; it is, however, 
estimated at an inch in thirteen minutes. In man, their 
entire length may be estimated at about the -^3- of an 
inch, the length of the head being about the 5() l 00 ^ and 
its breadth the l0 ^ Q0 . They continue to exhibit mo- 
tion in birds for fifteen or twenty minutes after death ; 
in cold-blooded animals even after days. 

In man, the production of spermatozoa commences 
between the fourteenth and sixteenth year, the time of 
puberty, and continues until the sixty-fifth or seventi- 
eth, or even much longer. This period of commence- 
ment is marked by a great change in the physical and 
moral constitution. 

2d. Of the Germ-cell. — In mammals the female repro- 
ductive apparatus consists essentially of the ovaries, ovi- 
duct, and uterus. 

The ovaries are two ovoid bodies situated on either 
side of the uterus. The}*- consist of a stroma in which 
vesicles are imbedded : these vesicles give origin to the 
ova. In the manner to be presently described, the ova, 
being received at the fimbriated extremities of the Fal- 
lopian tubes, those tubes being therefore appropriately 

What are the spermatozoa? What is the mode and rapidity of 
their motions ? What is their size ? How long may they continue 
their motions? At what time do they first appear? What are the 
essential parts of the mammal reproductive apparatus ? What are 
the ovaries ? 



OVUM IN THE OVAKY. 339 

termed oviducts, are carried into the cavity of the ute- 
rus. 

At the time of puberty in the human female, which 
occurs between the 14th and 16th year, a physical and 
moral change takes place, answering to that already al- 
luded to as occurring in the male. From this period a 
sanguinolent discharge makes its appearance monthly: 
it is the catamenia. The interval from time to time is 
commonly estimated at four weeks ; it varies, however, 
with individuals, and it is said also with climates, the 
discharge occurring in the hotter more frequently, and 
in greater quantity. It is essentially blood, deprived of 
its quality of coagulating by intermixture with acid mu- 
cus of the vagina. So long as these periods continue, 
the individual possesses the reproductive power, the first 
appearance of the catamenia indicating the capacity for 
conception, and the disappearance, at about the 45th 
year, its end. During gestation the catamenia are sus- 
pended, and, indeed, it is this event which is usually 
taken as the indication that conception has occurred. 

I. Ovum in the Ovary. 

The ovary is the organism in which the ova are pre- 
pared, these bodies arising in the following way : 

In the stroma of the ovary there occur at a time ten, 
twenty, or many more cells. They have received the 
designation of Graafian vesicles or ovisacs. They orig- 
inate in the interior of the ovary, and, as they become 
perfected, pass to its surface, presenting themselves 
thereupon as prominences covered over exteriorly with 
peritoneum. Each of these vesicles has a membranous 
envelope connecting it with the substance of the ovary 
exteriorly, and covered interiorly with a layer of nucle- 
ated cells, designated membrana granulosa. It is filled 
with a fluid in which multitudes of granules float, and 
in its centre is the ovule. This, as it becomes mature, 
is pushed up toward the surface of the ovisac by an ac- 
cumulation of liquid in the lower part thereof, and is so 
brought into close relation with the membrana granu- 
losa at the place where it is upon the surface of the ova- 
ry. At this point there collects on the ovum a zone of 

What is the catamenia! discharge? How long floes it continue? 
What does it indicate? Describe the production of ova. 



340 



OVUM. 



granules, to which the designation of discus proligerus 
is given. 

Fig. 129, transverse section through the ovary: a, 
Graafian follicle of inferior, and, 6, of superior surface ; 
c, peritoneal lamella of ligamentum latum, continued 
upon the ovary, and coalescing with, d x the tunica albu- 
ginea : in the interior two corpora albicantia (old cor- 
pora lutea) are visible ; e, stroma of the ovary. 



Fig. 131. 




Section of Graafian vesicle. 



Ovum. 



Section of ovary. 

Fig. 130, section of the Graafian vesicle: 1, stroma 
of ovary, with blood-vessels; 2, peritoneum; 3 and 5, 
layers of the external coat of the Graafian vesicle ; 4, 
membrana granulosa ; 6, fluid of the vesicle; 7, granular 
zone, or discus proligerus ; 8, the ovum. 

Fig. 131, ovum: 1, germinal spot; 2, germinal vesi- 
cle; 3 yolk; 4, zona pellucida; 5, discus proligerus; 6, 
adherent granules or cells. 

The diameter of the human ovum varies from the y^ 
to the -2^0" °f an inch. It consists of an exterior trans- 
parent membrane, the 25 x 00 of an inch in thickness, 
which, when compressed for the purpose of examina- 
tion, appears like a diaphanous circle, and hence called 
zona pellucida. Within this zone, and inclosed by it, 
is the yolk, a granular material suspended in or inter- 
mingled with fluid, the granules being of different sizes ; 
those near the pellucid zone are the largest. For the 
most part, the yolk consists of albumen and oil globules. 
Its condition, as regards liquidity, varies in different an- 
imals ; in some it is almost a soft solid, so that, when 
water percolates through the zona pellucida, it isolates 

Describe Figs. 129, 130, 131. What is the size of the human 
ovum ? Of what parts is it composed ? What is the zona pellucida ? 



DIAGRAM OF GRAAFIAN VESICLE. 



341 



the yolk by surrounding it on all sides, and parting it 
off from the zone. Within the substance of the yolk is 
a distinct cell, the germinal vesicle, which gradually 
makes its way from the interior to the place of perito- 
neal contact. As it advances to perfection, it consists 
of a delicate spherical membrane containing a liquid, in 
which granules are suspended. Upon that portion of it 
nearest to the place of peritoneal contact is its nucleus, 
the germinal spot, about the ^oVo °f an inch * n diame- 
ter, and consisting of yellow granules. 

Ft'j. 182, diagram of a Graafian vesicle and ovum : 1, 

Fig. 132. 




Diagram of Graafian vehicle. 

stroma of ovary; 2, 3, external and internal tunics of 
the Graafian vesicle ; 4, cavity of vesicle; 5, thick tunic 
of the ovum or yolk-sac; G, the yolk; 7, the germinal 
vesicle; 8, the germinal spot. 

The most mature ova are nearest the surface of the 
ry, but are separated from its peritoneum by a thin, 
fibrous layer of stroma. The Graafian vesicle is, there- 
fore, the parent of the ovum. Periodically, at the cata- 
menia, as development is going on, the Graafian vesicle 
bursts, and the ovum is set free. This effect arises, in 
part, from the circumstance that, the space between the 

How frequently do the Graafian resides burst 
and discharge ova ? 



342 OVUM IN THE OVIDUCT. 

vesicle and ovum being filled with cells, those near the 
surface of the ovary disappear, and an albuminous liquid, 
accumulating below, pushes the ovum up. The ovisac, 
or Graafian vesicle, thus changed into a follicle, is grad- 
ually filled up, its walls wrinkling, and red-colored ma- 
terial, arising from the membrana granulosa, being de- 
posited in it until it is almost filled. This deposit grad- 
ually turns yellow, and is eventually composed of cells in- 
teriorly, and fibres arising therefrom exteriorly. When 
the deposit is completed, a stellated cicatrix is observed 
in its midst. The yellow body thus arising passes un- 
der the designation of corpus luteum. If impregnation 
does not occur, the yellow substance forms to but a 
small extent, and after a time disappears. An ovum is 
therefore discharged at each monthly period. 

II. Fertilized Ovum in the Oviduct. 
Such being a description of the ordinary or unfertilized 
ovum, we have next to follow the changes ensuing if fer- 
tilization has taken place. 

The spermatozoa having become enveloped in the 
pellucid zone or passing through it, the ovum is re- 
ceived by the fimbriated extremities of the Fallopian 
tube, along which it is carried by peristaltic contraction 
or ciliary motion. The first change taking place in it is 
the disappearance of its germinal vesicle and germinal 
spot. This disappearance is, however, stated by some 
to be preceded by a development of cells originating 
in the nucleus or germinal spot ; nor is it the result of 
fertilization, since it occurs in the 
unimpregnated ovum. The cells 
of the membrana granulosa, sur- 
rounding the ovum, become first 
of a conical shape, but their round- 
ed form is resumed on passing into 
the tube. 

Fig. 133, ovarian ovum of dog, 
exhibiting the elongated form and 
stellate arrangement of the cells 
Ovarian ovum. f the discus proligerus round the 

zona pellucida. 

What is the corpus luteum? What is the first change taking 
place in the fertilized ovum ? Describe Fig. 133. 




SEGMENTATION OF OVUM. 



343 



Ovarian Omm. 



Fig. 134, same ovum after the re- 
moval of most of the club-shaped cells. 
The yolk is next observed to con- 
yfl ^^y tract so as to leave a clear space be- 
A j^L ^ ween ft aiK ^ * nc zona pellucida. As 
fl V t^? the passage along the tube is taking 
<< ^ ^/ place, the zona assumes a coating of 
albuminous material ; this is what is 
called in birds the white of the egg. 
It eventually becomes the chorion. 
Meantime, after the disappearance of the germinal vesi- 
cle, a new cell, the embryo cell, arises, and this under- 
goes subdivision or segmentation, an eiFect in which 
the yolk itself presently becomes involved, each new or 
daughter embryo cell so arising assuming a part of the 
yolk. A constant process of bisection is thus establish- 
ed, the yolk dividing first into two portions, then into 
four, eight, sixteen, etc., each division containing a nu- 
cleated cell. At this period may be seen the sperma- 
tozoa involved in the zona pellucida, and, as the process 
of bisection goes on, the mass assumes a mulberry as- 
pect, and finally becomes granular. This is, for the most 
part, finished by the time the ovum enters the uterus. 



Fig. 135. 




Segmental k-n of OVOID. 



I) scribe Fig, 184. If m does the mulberry mass arise? When 

is (he pro _ mentation finish 



344 THE GERMINAL MEMBRANE. 

Fig. 135, p. 343, ova of the dog in various stages : a, 
from the oviduct, half an inch from the uterus, spernia- 
tozoids being in the pellucid zone, the yolk bisected ; 6, 
cells of tunica granulosa have disappeared, and the yolk 
is in four segments ; c, continued advance in segmenta- 
tion ; dj the zona has become thicker, and the segmen- 
tation more complete ; 6, ovum burst by compression : 
some of the segments have escaped; each shows a bright 
spot or vesicle. 

As the ovum is about to enter the uterus, each por- 
tion arising from the segmentation of the yolk has be- 
come a perfect cell. This cell formation having been 
accomplished at the surface of the yolk first, the cells 
there begin to coalesce into a membrane, with an aspect 
like that of hexagonal pavement epithelium, and, as the 
change passes toward the centre, the cells, as they form, 
come toward the membrane and thicken it, leaving a 
clear liquid within. In this manner a secondary vesicle 
forms within the zona pellucida : it is the blastodermic 
vesicle : it is the temporary stomach of the embryo. Its 
wall constitutes the germinal membrane, upon which the 
embryo arises. New cells being constantly added, the 
membrane increases in thickness ; and here it may be re- 
marked that, in most types, the yolk is to be considered 
as presenting two portions — the germ-yolk and the food- 
yolk; the former being immediately employed in the 
development of the embryo, and the latter being a stock 
for more advanced supply. In mammals, for whom other 
means of nutrition are quickly provided, the food-yolk is 
imperceptible, and, moreover, in them the albuminous 
coating of the zona pellucida is small; and in birds, the 
embryo of which has to be nourished independently of 
the parent, the quantity is necessarily large. As we have 
said, this albuminous covering and the zona together 
constitute the chorion, the exterior of which presents a 
rugged aspect, from the appearance of absorbing radi- 
cles, which, becoming imbedded or dove-tailed in the 
deciduous membrane, presently to be described, estab- 
lishes the necessary connection for tuft nutrition, and 
thereby obtaining albumen from the parent. 

What becomes of each portion of the segmented mass? How 
does the blastodermic vesicle form ? What is its use ? What is the 
germinal membrane ? What are the uses of the two kinds of yolk ? 
In what manner does the chorion form ? 



UTEEIXE XUTEITIOX. 



345 






III. Fertilized Ovum in the Uterus. 

While the ovum is passing through the Fallopian tube 
or oviduct, it obtains a coating of albuminous material 
outside of its zona pellucida. This coating becomes the 
means of attachment to the uterus, and thereby of the 
absorption of nutriment in the following way. 

The outside surface of the incipient chorion presents 
a layer of cells, and soon after assumes a fibrous struc- 
ture*. In this condition the ovum makes its appearance 
in the uterus, on the interior of the surface of which the 
mouths of a great number of folli- 
cles open. Their general appear- 
ance is illustrated by Fig. 136 ; (7, 
ca3cal terminations of glands ; e, 
their tubes ; a, mouths on interior 
of uterus. The constitutional dis- 
turbance at this time taking place, 
enhanced by the presence of the 
ovum in the organ, at once in- 
creases its vascularity; the follicles 
become larger, cells are abundant ly 
developed in them, and the uterine 
cavity is filled with a liquid con- 
taining many nucleated cells. This 
plastic semi-fluid material receives 
the fringes of the villous coat of 
the chorion, now being developed ; 
and these even find their way into 
the mouths of the glandular tubes; 
from this exudation or secretion the 
membrana decidua forms, though 
by some it is represented as being 
" tubeJ - a metamorphosis of the mucous 

membrane itself. Meantime the ovum is coated over 
with a c oding membrane, designated membrana 

ret! it was believed to originate in the cir- 

camstance that, when the ovum reached the uterine 
nth of the Fallopian tube, it there encountered the 
rr membrana decidtfa, and, not perforating it, but 
ingil onward, gathered a fold, covering, or envelope. 

What l:;*; illustrate? la what manner docs the decidu- 

ous membrane form ? 

P2 




346 MEMBRANA DECIDUA AND PLACENTA. 

It is, however, now admitted that this description of the 
formation of the membrana reflexa is erroneous, for in 
reality the ovum is at no time on the outside of the mu- 
cous membrane, which is continuous from the cavity of 
the uterus through the Fallopian tube. The following, 
therefore, seems to be the more correct description. The 
presence of the ovum gives rise to an increased develop- 
ment of cells, rapidly spreading around it, and coating it 
all over, their points of origin being those portions of the 
uterine mucous membrane with which the ovum is in 
contact. In this way it receives its deciduous envelope, 
which, participating duly in its growth, is at the end of the 
third month in contact with the uterine deciduaall over. 

At the stage we are now considering, the nutrition of 
the embryo is conducted in a special but very temporary 
way. The yolk of the ovum has no stock of food to 
maintain the nutritive processes beyond the brief space 
transpiring in the passage through the Fallopian tube. 
The duty of nutrition is at .this moment assumed by the 
villous coat of the chorion : this absorbs fluid exuding 
from the uterine decidua very much after the manner of 
the spongioles of a plant ; but almost immediately the 
necessity arises of diverting more directly the albumi- 
noid material to the quickly-growing embryo from the 
yolk-bag, to which it would have gone, and this new 
destination implies the introduction of new channels of 
transport, which, under the form of a vascular appara- 
tus, are now provided. 

About the close of the second month, a proper vas- 
cular apparatus for the combined purposes of nutrition, 
secretion, and respiration makes its appearance: it is the 
placenta. Its origin is in the little blood-tubes forming 
in the tufts of the chorion, in man at one point, in rumi- 
nants simultaneously at several, and giving rise in the 
former case to one organ, the placenta, as has been said, 
in the other to many such, or, at all events, to one of a 
composite structure, the cotyledons. The foetal vessels 
thus arising in the villi of the chorion become inter- 
mingled with vessels contemporaneously arising from 
the uterus; and though, in some cases, this intermin- 
gling is less complicated, so that the maternal and foetal 

What changes occur at this period in the nutritive process ? In 
what manner does the placenta arise? 



DIVISION OF THE GERMINAL MEMBRANE. 



347 



portions are separable, in man the internetting is com- 
plete, the principle being to bring the foetal vascular tufts 
in such a relation with the maternal blood-sinuses, by 
the tufts dipping down or being enveloped therein, that 
the completest contact and facility of exchange, but not 
of intermixture, may be insured. Things are arranged 
in such a way that the maternal and foetal blood do not 
intermingle, each being confined in vessels of its own, 
through the thin walls of which nutritious matter may 
pass and excremeutitious matter repass. Every foetal 
tuft has a deciduous layer upon it, and the blood brought 
by the curling arteries of the uterus furnishes to the foe- 
tus its oxygen, and receives back carbonic acid, with 
other excrementitious matters. In this respect, respira- 
tion is carried on by the aid of a mechanism answering 
to the gills of fishes, the maternal arterial blood stand- 
ing for the aerated water ; but, besides this, the tufts 
have another duty to discharge — the obtaining of albu- 
minoid material from the maternal blood. The placen- 
tal mechanism is therefore much more perfect in its ac- 
tion than the tuft mechanism preceding it. 

The germinal membrane, formed as has been de- 
scribed, already exhibits at one spot an opaque area of a 
roundish shape, consisting of 
cells and granules. To this 
the designation of germinal 
area is given. At this area 
the membrane next becomes 
divisible into two laminae, 
and eventually throughout 
its whole extent, as seen in 
Fig. 137. Of these laminae, 
the exterior, nearer to the 
zona pellucida, is the serous 
layer. It is the raised mem- 
brane of the figure, and in it 
are to be developed the nerv- 
ous and muscular systems of the embryo. The interior 
i- designated the mucous layer, and from this arise the 
digestive organs. 

What are its functions? "What layers next arise in the germinal 
membrane? What systems arise from its serous layer? What sys- 
tems from its mucous? Describe Fig. 137. 



Fig. 137. 




The germinal area. 



348 



THE CEREBRO-SPINAL AXIS. 



The germinal area by degrees loses its circular form 
and becomes oval, its central portions clearing off and 
giving rise to the area pellucida. Around this the opac- 
ity is increased, and in it blood-vessels appear ; hence to 
this dark circle the designation of area vasculosa is ap- 
plied. In the pellucid zone is next seen a delicate line, 
the primitive groove, Fig. 138: a, area pellucida; 6, 



Fig. 138. 




The primitive groove, magnified 8 diameters. 

dorsal laminae ; <?, primitive trace. It occurs in the se- 
rous layer only, is wider at one end than at the other, 
the wider part being destined for the head of the em- 
bryo. On each side of the primitive groove two oval 
areas of c&lls emerge : they are the dorsal laminae. They 
rise up to cover in the primitive groove, so as to con- 
vert it into a tube, with three bead-like swellings at its 
wider end, the elements of the prosencephalon, mesen- 
cephalon, and epencephalon, Fig. 139 : a, cephalic end ; 
#, chorda dorsalis ; c, vertebra ; c?, dilatation. On the 
internal part of the lamina nervous matter begins to 
form, the rudiment of the cerebro-spinal axis. In the 
bottom of the groove is the trace, chorda dorsalis. The 
groove its elf, converted into a tube, constitutes the cen- 

Describe Figs. 138, 139. In what manner does the cerebro-spinal 
axis arise ? 



VERTEBRAL COLUMN. 
Fig. 139. 



349 




Origin of the brain upon the spinal cord, magnified 8 diameters. 



tral canal of that axis, its completion into the tubular 
shape occurring first in the middle, and then up and 
down. The form of the lateral masses varies as devel- 
opment goes on. 

A line of cells running lengthwise in the primitive 
groove is the origin of the chorda dorsalis, on which the 
rudiments of the vertebral column appear. In the am- 
phioxus and myxenoid fishes development in this direc- 
tion stops at this point, the chorda dorsalis being the 
permanent structure. The vertebrae now emerge under 
the aspect of square plates, and the dorsal lamina}, pro- 
longing themselves outward and downward, as it were, 
by an offshoot, produce the ventral laminae; which close 
in the abdominal walls, and so form the boundaries of 
the trunk. Simultaneously a new layer of cells arises 
between the serous and mucous layer of the germinal 
membrane, at the; area vasculosa, and in this intercalated 
lamina the vascular system forms and blood corpuscles 
appear, capillary vessels arising from tin; coalescence of 
nucleated cells, the touching ends of which become per- 
vious. A- the i forward, a net work of such 
is constructed, and it i^ to he particularly re- 
are the vertebra produced? In what manner arc the blood- 



350 ELEVATION OF THE EMBRYO. 

marked that this takes place and that the blood is in 
circulation prior to the existence of the heart. Around 
the extending blood-vessels or vascular area runs a cir- 
cular capillary called the terminal sinus in the first stage 
of the process, but this disappears as the vessels extend 
all over the germinal membrane. The extension of these 
vessels is in part accomplished by the cells from which 
they have arisen elongating themselves into processes. 

The heart appears first as a canal or tube, arising in 
the vascular layer from a columnar mass of cells, of which 
the inner ones have deliquesced to form a tube. This 
then becomes tri-chambered, containing an auricle, a ven- 
tricle, and the bulbus arteriosus. Subsequently the au- 
ricle and ventricle are each divided by septa, that in the 
ventricle being commenced about the fourth, and finished 
about the eighth week. The auricular septum is not 
completed until after birth. 

Fig. 140 shows the human heart at about the fifth 
week: A, the heart opened on the abdominal aspect; 1, 

the bulbus arteriosus ; 2, 2, 
two aortic arches, uniting 
posteriorly to form the aor- 
ta; 3, the auricle; 4, the open- 
ing from the auricle into the 
ventricle, 6, which is laid 
open ; 5, the septum rising 
from the lowest part of the 
cavity of the ventricle ; 7, 
the vena cava inferior : B, 
view from behind ; 1, the 
trachea; 2, the lungs; 3, the 
ventricle ; 4, 5, the large atrium cordis, or auricle ; 6, the 
diaphragm ; 7, the aorta descendens ; 8, the pneumogas- 
tric ; 9, its branches ; 10, its continuation. 

As soon as the capillary system is fairly established, 
the change in the character of the function of nutrition 
alluded to is accomplished, and in those animals depend- 
ing for their development on a food yolk, it is eventually 
entirely covered with ramifications of these vessels. The 
blood-cells of the first order or series are evolved from 
the nuclei of the cells which coalesced for the formation 

of blood-vessels. 

Describe Fig. 140. 




Foetal heart. 



HIE INTESTINAL CANAL. 351 

The development of the embryo still continuing, it 
assumes a form aptly described as resembling that of a 
boat placed upside down, the bottom of the boat rising 
higher and higher above the surface of the germinal 
membrane, and lifting with it that portion of the mem- 
brane to which it is attached. The two ends of the 
boat-shaped body bend under toward one another; the 
larger of the two is destined to become the head of the 
embryo. As this elevation takes place, the embryo be- 
comes separated by a constricted space from the sur- 
rounding germinal membrane, its abdominal parietes be- 
ing still open and in contact with the yolk. From the 
layer thus lining the interior of the cavity of the embryo, 
the intestinal canal arises as a tube from the coalescence 
of a pair of lateral ridges, and the surrounding and ex- 
terior portions of the germinal membrane, elevating 
themselves above the constricted space", coalesce over 
the back 6f the embryo, and thus inclose it in a sac. 
This sac constitutes the amnion, and in this manner, by 
folding, the interior of the germinal membrane is used 
as a digestive surface, the outer as one for secretion. 
The umbilical cord obtains a sheath from the amnion, 
which at one end is continuous with the skin of the foe- 
tus, and the other is reflected over the surface of the 
placenta. The amnion therefore constitutes a closed sac, 
containing a fluid, the liquor amnii. 

The place at which the germinal membrane is con- 
stricted, so as to be able to act as a digestive surface to 
the embryo, though linear at first, is gradually narrowed 
down, and constitutes the umbilicus. This constricted 
part is now the omphalo-mesenteric duct. It communi- 
ty with the cavity of the yolk-sac, which, at this stage 
<>f development in mammalia, is the umbilical vesicle. 
In birds, the yolk-sac is carried completely into the ab- 
domen through the umbilical opening; in mammals it 
a lins exterior. It does not appear that the contents 
of the yolk are directly absorbed from the cavity of the 
. but they are carried by the ramifying vessels to the 
liver. These vessels are therefore counterparts of the* 
9enterio. Eventually folds arise on the lining mem- 

In what manner is the embryo developed a- a boat-shaped body? 

a the amnion form? How docs the intestinal canal a: 
What becomes of the yolk-sac in birds and mammals respectively? 



352 THE CIRCULATORY SYSTEM. 

brane of the yolk-sac over which these vessels pass, and 
facilitate absorption. In fish, at this stage, the yolk-bag 
hangs clown, and respiration takes place upon its surface. 

From the caudal extremity of the embryo the allantois 
emerges as a mass of cells, the interior liquefy, and the 
exterior then constitute a sac. In birds and in reptiles 
it reaches considerable development; in the former ex- 
tending entirely over the yolk-sac, but in mammals it is 
soon replaced and shrivels up. It discharges the func- 
tion of a urinary bladder, and, indeed, a portion of it 
continues to do so in man. Its disappearance is the sig- 
nal that the embryo is now depending on the placenta. 

To return now to the development of the circulatory 
system. At about the end of the eighth week, as we 
have seen, the ventricle is divided by a septum, the di- 
vision of the auricle not occurring till a little after, and 
even then not*being perfect, an aperture, the foramen 
ovale, existing. This is the state of things at about the 
twelfth week : of the five branchial arches two disap- 
pear, the aortic bulb then divides into two tubes, which 
are to be the aorta and pulmonary artery respectively. 
Next, one of the branchial arches forms the subclavian 
and carotid arteries. Of the middle pair, the right is 
obliterated, but the left remains to constitute the arch 
of the aorta. Of the lowest pair, the right forms the 
right and left pulmonary arteries, and the left consti- 
tutes the ductus arteriosus. 

The blood-system having reached its full development, 
the fcetal circulation maybe described as follows: From 
the placenta oxidized blood is brought through the um- 
bilical vein, a part passing into the ascending cava through 
the ductus venosus, and the rest into the liver through 
the vena portse, from which, by the hepatic vein, it also 
reaches the ascending cava. In its passage to the heart 
it becomes adulterated with blood derived from the 
trunk and lower extremities. It next goes into the 
right auricle, and, to some extent, is kept from contam- 
ination with the venous blood coming through the de- 
scending cava by means of the Eustachian valve, which 
directs the arterialized blood through the foramen ovale 

What is the first appearance of the allantois ? Describe the order 
of development of the circulatory system. Describe the fcetal circu- 
lation. 



DEVELOPMENT OF OEGA1S1SM. 353 

into the loft auricle, from which it gains the loft ventri- 
cle, and also directs the venous blood of the descending 
cava into the right ventricle. The blood in the left ven- 
tricle is driven therefrom into the ascending aorta, and 
supplies the head ; but the venous blood in the right 
ventricle is driven therefrom through the pulmonary 
artery and ductus arteriosus into the descending aorta, 
and, mingling with the arterial blood therein, passes to 
the trunk and legs. Of this blood a portion is then car- 
ried to the placenta to be arterialized. 

From the description thus given, it may be gathered 
that, up to the period of birth, three distinct types of 
nutrition have been followed. They may, with sufficient 
accuracy, be designated, 1st. Yolk nutrition; 2d. Tuft 
nutrition ; 3d. Placental nutrition. To these may be 
added the two followed at a later period; 4th. Lacta- 
tion, and, after the dental mechanism is sujDplied, 5th. 
The diet of mature life. 

During the development of any new 7 organism, the 
new parts uniformly arise from the old ones; they are 
not built from foreign materials depositing themselves 
upon new centres, but are educed by the unfolding, en- 
larging, and modeling of parts already existing. An 
organism is not developed as we enlarge a house, by 
building part to part, but it all expands from one com- 
mon or single centre. As the sphere of its expansion 
becomes greater, the opportunity arises for devoting dif- 
ferent regions to different uses, and thus offices which 
were confusedly intermingled become separated out, and 
as, in social undertakings, the division of labor gives 
iter perfection to the work, so in this, functions 
which, because they were blended, were imperfectly dis- 
charged, now assume precision and power, because they 
are disentangled from what were perhaps countervailing 
conditions. 

By these considerations, we are gradually led to the 
era! law of development, first recognized by Von Bar, 
and ; under his name. This is somewhat obscure- 

ly enunciated in the following terms: "The heterogene- 
ous the homogeneous by a gradual process 
of change." By this it is meant that, in the proc< ^s of 

How many different types of nutrition are there? In what man- 
ner do now parts arise? What is the law of Yon liar? 



354 APPARATUS OF ORGANIC LIFE. 

development, the stages are not from forms that are of 
a degraded to those of a higher type, but that from the 
general the special, which was therein included, is grad- 
ually evolved. 

Respecting the development of special organs, it may 
be remarked that of the permanent ones, the vertebral 
column is one of the first to appear ; it shows itself un- 
der the form of isolated quadrangular elements. The 
gelatinous cellular structure, chorda dorsalis, acquires a 
sheath, which assumes a fibrous structure, and from this, 
in the lower vertebrates, the vertebrae are evolved. In 
man, the elementary quadrangular plates are considered 
to have an independent origin. As they increase in 
number and size they surround the chorda, and projec- 
tions springing from their superior surface form arches 
to envelop the spinal cord. Each vertebra, therefore, is 
constructed by the union of two pieces, one on either 
side. These first assume the condition of cartilage, and, 
later, the body and arches ossify from separate points. 
The chorda dorsalis, which has, during this development, 
been gradually evolved in the bodies of the vertebrae, 
disappears. 

The bones of the skull are metamorphosed vertebrae, 
of which four appear to have undergone change. To 
these the auditory, gustative, optic, and olfactory nerves 
are respectively related, in the same manner that the 
spinal nerves are to their vertebrae. 

In the descriptions given in the preceding part of this 
work, incidental allusion to a sufficient extent has been 
made to the development of most of the apparatus of 
organic and also animal life. It may therefore here be 
briefly stated that the alimentary canal originates in the 
pinching off of a part of the blastodermic vesicle below 
the spinal column. At first it is a straight tube, com- 
municating about its middle with that vesicle, but after 
a time showing its eventual division into oesophagus, 
stomach, large and small intestines, assuming an oblique 
position on the part to be occupied by the stomach, and 
then curving in the region of the intestine. From a part 
of this tube the liver emerges as a thickened deposit of 

How is the vertebral column developed ? From what do the bones 
of the skull originate ? How does the alimentary canal arise ? What 
is the origin of the liver ? 



INDICATIONS OF CONCEPTION". 355 

cells, into which the wall of the intestine bulges so as to 
form a kind of sac, and from this rudiment a ramified 
structure arises, which at last recedes from its place of 
origin, and is connected with the intestine by the hepatic 
duct. The commencement of this structure is about the 
third week, but it proceeds with so much rapidity that 
in the third month it nearly fills the abdominal cavity. 
The functions of the liver at this period have already 
been pointed out, the meconium it secretes being modi- 
fied bile. In like manner, from the digestive tract, the 
pancreas and salivary glands originate from masses of 
cells, ducts being formed by deliquescence of portions 
within. From the alimentary canal, also by budding and 
deliquescence, the lungs arise, their cavity communica- 
ting at first by several apertures with the pharynx. This 
occurs about the sixth week. These organs are gradu- 
ally removed from the place of origin, as in the case of 
the liver. 

The Wolffian bodies are temporary urinary organs, 
preceding the kidneys, and eventually disappearing. 
They are of an ovoid shape, and consist of a duct from 
which transverse canals branch forth, the duct discharg- 
ing into the sinus urogenitals. They originate about 
the end of the first month, and commence to degenerate 
in the third. In fishes they remain as the permanent 
urinary apparatus. The testes or ovaries arise from the 
inner margin of the ^Wolffian body, the former being 
guided into the scrotum by the gubernaculum. This de- 
scent commences between the fourth and fifth month, 
and is completed at birth or shortly after. 

Among the indications that conception has occurred 
are usually enumerated, stoppage of the menses, the pla- 
cental murmur, the development of the mammary gland, 
its sense of pain or tenderness, the color of the areola, 
the turgescence of the areola and nipple, irritability of 
the stomach. Quickening, as it is termed, usually oc- 
curs about the eighteenth week, and parturition in the 
fortieth, or at the close of 280 days. With respect to 
this, it is admitted that the term may be possibly pro- 
longed, in very rare cases, by 40 days. The French laws 

What substance doee it at tbi< early period secrete? How do the 
longs What i- the function of the Wolffian bodi< b? What 

are the signs of concept] 



356 INFLUENCE OF BOTH PARENTS. 

legitimatize a child born within 300 days ; and that such 
variations of the proper term may occur is proved by 
observations made upon domestic animals, in which the 
duration of pregnancy can be ascertained with precision. 
In the cow, which has the same period of gestation as 
the human female, the shortest period hitherto observed 
is 213 days, the longest 336. The shortest period at 
which human parturition can occur, consistent with the 
viability of the child, appears to be about 23 weeks. 

The act of parturition in its first stage is to be refer- 
red to a contraction of the muscular fibres of the fundus 
and body of the uterus with a synchronous relaxation of 
those of the cervix. At a later period the contraction 
of the expiratory muscles assists. After birth is accom- 
plished, the mouths of the uterine vessels are closed 
through the contraction of the organ, the lochial dis- 
charge carrying with it any disintegrated residues of 
the deciduous membrane, and also large quantities of 
fat, derived probably from the degeneration of the uter- 
ine structure itself. 

That both parents are concerned in imparting charac- 
teristics to the child there can be no doubt : it is fully 
established where they are of different races, as white 
and black, or white and red ; and equally in the case of 
animals, as in mules, produced by the mixture of differ- 
ent kinds. It is scarcely necessary to remark that this 
extends to the communication of more refined peculiari- 
ties, the resemblance of countenance, figure, gesture, and 
even mental qualities, family likenesses we daily observe. 
These impressions are of a much more profound charac- 
ter than might at first be supposed, as is proved by the 
fact that the third generation will exhibit peculiarities 
belonging to its progenitors, though those peculiarities 
have not occurred in the second. 

What is the period of gestation ? In what manner is the act of 
parturition accomplished ? What does the lochial discharge remove ? 
How is it certain that both parents impart characteristics to the 
child? 



THE EARLIEST PERIOD OF LIFE. 



CHAPTER XXIV. 

THE GROWTH OF MAX. 

. — Wt igh t \ — TT igh t 

I Period*. — Develops 'the 

In U ttect. — Maturity of Man. 
Mi • — Mortality at dt 

P ' " tfljCfe. — Uructurej Rmctions^ 

! Mortality of the he 

At birth, the human infant is the very representative 
of weakness and imbecility. Though, unlike many other 
mammals, it opens its eyes at once, it exhibits no tokens 
of visual perceptions ; though it may be subjected to 
sounds or noises of various kinds, it takes no notice 
whatever of them. This condition of inertness is fol- 
lowed by a condition of confused sensation, which by 

2 zees is succeeded by a capability of appreciating spe- 
cial ideas. The earliest period of conscious existence is 
a scene of pain, the life of the infant being divided be- 
tween sleep and crying; from its slumbers it is awakened 
only by the pains of hunger ; nor is it until after the lapse 
of many days, or even weeks, that the first smile is seen. 
It is too feeble to turn from side to side, but remains in 
the position in which it was placed. Its skin at birth 
covered over with a whitish incrustation, the vernix ea- 
seosa, becomes reddish; the depth of this tint, however, 
shortly away. At this period, moreover, life is 

pur _ . the infant feeding and sleeping. The 

biliary matter, meconium, which had accumulated in its 
intestine during fata] life, is discharged in the course of 
a day or so after birth, and the digestive apparatus en- 
unctions with activity. 

it the infant smiles soon after it is forty 
days ol _rh it can cry it* can not shed tea- 

fore loi._ ktionfl of actions and 

likes r er of moving in an i jain- 

the human infant vi HXthf What is the 

vernix caseosa? What is mecon; 



358 THE TEETH — GROWTH OF THE SEXES. 

ed by it in the course of a year, and by the close of that 
time it c^n masticate. Of its teeth, the central incisors 
appear about the seventh month, those of the lower jaw 
first ; the lateral incisors about the eighth or tenth, the 
anterior molars about the twelfth, and the canines about 
the eighteenth, the posterior molars being cut between 
that time and three years. The average date of the ap- 
pearance of the permanent teeth is, the front molars 
about the seventh year ; middle incisors, eighth ; lateral 
incisors, ninth ; anterior bicuspids, tenth ; second bicus- 
pids, eleventh ; canines, twelfth to thirteenth ; second 
molars, twelfth to fourteenth ; and the last molars from 
the seventeenth to the twenty-first year. 

The power of articulate speech is displayed within 
twelve or fifteen months, some letters being more easily 
gained than others ; among them are A, B, P, M. 

Throughout infancy and childhood, the features, and 
even the gestures, indicate the profound constitutional 
changes going on. The countenance, instead of express- 
ing pleasure or pain in the aggregate by smiling or cry- 
ing, as was the case at first, gains the faculty of repre- 
senting every grade of feeling. Long before maturity is 
reached we read without difficulty the thoughts passing 
in the mind from the movements of the lip or the eye, 
and the painter can express every shade of feeling, and 
every emotion, by the mere configuration of the outward 
form. 

The monthly growth of the foetus for six months be- 
fore birth is about two inches. At birth, the mean length 
of boys is 18 J inches, and of girls 18^ inches, the former 
being therefore a little the longer. 

At sixteen or seventeen years the growth of girls is 
relatively as much advanced as that of youths of eight- 
een or nineteen. For the most part, the inhabitants of 
towns are taller than those of the country. The full 
height is not reached, in some instances, until twenty- 
five years ; in very warm and very cold climates it is 
more quickly attained. The recumbent position is re- 
garded as being favorable to growth, and, influenced by 

How long is it before the teeth are cut ? What is the order of their 
appearance? What letters are first articulated? What is the mean 
length at birth? What is the growth of boys and girls relatively to 
each other? When is the full height reached ? 



MAXIMUM AND MINIMUM OF HEIGHT. 359 

his own weight, an individual is shorter in the evening 
than when he lirst rises from bed in the morning. 

With regard to the rate of growth, it is most rapid 
immediately after birth, and continually diminishes until 
about five years, the epoch of maximum of probable life. 
It then remains equable to about sixteen years, the an- 
nual growth being 2-1 inches. After puberty it declines, 
being, from sixteen to seventeen years, lj inches, and 
during the next two 1 inch only. The annual increment 
relatively to the height then attained continually dimin- 
ishes from birth. The foetus grows as much in length 
in a month as the child from 6 to 16 years does in a year. 
The limits of growth of the two sexes are unequal, be- 
cause women are smaller than men, terminate their 
growth sooner, and annually grow less. Individuals in 
affluent circumstances may often surpass the standard 
height, but misery and fatigue are liable to produce the 
opposite effect. Longevity is generally less for persons 
of great height. 

Aa to the maximum and minimum of height, it may 
be remarked that Frederick the Great had a Swedish 
body-guard whose height was eight feet three inches ; 
and, on the other hand, Birch states that there was an 
individual, 37 years old, whose height was sixteen inches. 
In view of these and other such facts, Quetelet fixes on 
8 feet 3 inches as the maximum, and 1 foot 5 inches as 
the minimum of height ; he gives as the mean 5 feet 4 
inches. Half the men of France, at the age of conscrip- 
tion, are between 5 feet 2 inches and 5 feet 6 inches, but 
the wars incident on the great Revolution made a per- 
manent impression on the French in this respect by 
lowering the standard through the consumption of the 
taller men. M. Quetelet moreover remarks, that in ten 
millions of men there is but one more than G feet 8 inches, 
and one less than 4 feet. There is reason, however, to be- 
lieve that this statement will not hold good of America. 

A- regards weight, new-born boys are heavier than 

girls. An average taken from 20,000 gives 6 j lbs. as 

weight at birth ; the maxima and minima have been 

10£ lbs. and 2\ lbs. For about a week after birth the 

weight diminishes, owiiig to the effed of aerial respira- 

What are the maxima ami minima of height ? What is the mean 



360 MENTAL AND PHYSICAL DESCENT. 

tion. The difference in weight between the two sexes 
gradually diminishes until about the twelfth year, when 
an equality is reached. The maximum weight is at- 
tained about 40, and as 60 is approached a diminution is 
perceived, which reaches 12 lbs. at about 80 years, the 
stature likewise correspondingly diminishing by about 
2f inches; the female reaches her maximum weight 
somewhat later, at about 50 years. The extreme limits 
of weight in men are 108 lbs. and 216 lbs.; in women, 
87J lbs. and 206 J- lbs. The mean weight at nineteen is 
nearly that of old age in both sexes. At full develop- 
ment the male and female weigh almost exactly 20 times 
as much as at birth. In the first year the infant of both 
sexes triples its weight. It requires six years more to 
double that, and thirteen to quadruple it. Immediately 
after puberty both sexes have half their ultimate weight. 
Between the ages of 25 and 40 the mean weight of the 
male is 136^ lbs., and of the female 120| lbs. 

Arrived at maturity, the system of man commences to 
decline, the epochs of the maximum of physical and 
mental strength not, however, coinciding ; that for the 
former occurring at about the 25th year, but that for the 
latter not until between the 45th and 50th year. At 
this period, when the powers of imagination and reason 
have reached their highest degree, the liability to men- 
tal alienation and insanity is also at its maximum. 
Somewhat later, the physical system plainly betrays that 
it is pursuing its downward course, retracing the steps 
through which it passed forward to development. Soon 
there is an evident decrease of weight, the nutritive 
operations being no longer able to repair the waste of 
the body. There is also a diminution of the height. 
This corporeal decay is the signal for a depression of 
the mental powers, the first which begins to yield be- 
ing probably that of concentrating or abstracting the 
thought. As years pass on, external impressions exert 
a diminished influence, and he who at an earlier period 
reached the meaning of things, as it were, almost by 
intuition, now casts his eyes over page after page with- 

At what period is the maximum weight attained ? What are the 
limits of weight in men and in women ? When is the maximum of 
physical and of mental strength attained? What is the order of 
their 'decline ? 



7 



COMPARISON OF MORTALITY. 361 

out an idea being communicated to his mind. The old 
man querulously complains that he reads his book, but 
does not understand what it means. With this failure 
of perception the powers of memory decline, recent 
events lading away first, but those of early life being 
recollected longest. 

The mortality of towns is greater than that of the 
country. As we advance from the midst of the temper- 
ate region toward the equator or toward the poles, it 
also increases : thus, in the northern portions of Europe, 
the annual mortality is as 1 to 41 ; that of Central Eu 
rope, 1 to 40 T ^j ; that of Southern Europe, 1 to 33 
Considered as respects different periods of life, the rate 
of mortality varies very much. Of both sexes, 22 per 
cent, die before they are one year old, and 37 per cent, 
before they are five years old. Male infants are, how- 
ever, more liable to die immediately after birth than fe- 
male, but at the close of about two years their mortality 
is the same. Nine twentieths of the whole number born 
die before they are fifteen years of age, that is, before 
they have become useful to the community. 

The mortality among girls increases between 14 and 
13, and among men between 21 and 26. In France and 
Belgium, from 26 to 30 is the epoch of marriage, and at 
this period the mortality is the same in both sexes. It 
then increases for the women during the years of child- 
bearing, and afterward again becomes equal for both. 
At 25 years half the births are dead. The mean life 
may be estimated at 33 years. The maximum expect- 
ancy of life is at 5 years, at which age the risk of mor- 
tality is suddenly reduced, and becomes small till pu- 
iy, when, especially among girls, it becomes great. 
From 60 to 65 the chances of life are again at a min- 
imum. 

To the foregoing statements, in which contrasts have 
been drawn between the male and female, the following 
may be added : Not only is there a difference in the en- 
tire stature, but the different portions of the body have 
not the same relative size. The capacity of the skull in 
male is less; the body is longer; the lower ex- 

What is the mortality at different periods of life? What \s the 
relative mortality of the I ? What i- the difference in struc- 

ture of the male and female? 

Q 



362 PECULIARITIES OF THE FEMALE. 

trernities shorter ; the pelvis of greater size, especially 
in its transverse diameter ; the heads of the thigh bones, 
therefore, farther apart, and the bones themselves in- 
cluding a larger angle than in the case of the male; the 
chest and the abdomen are respectively more convex; 
the transverse diameter at the shoulders smaller, and 
the upper extremities, like the lower, shorter ; the hands 
and feet, fingers and toes, of less size. The surface pre- 
sents a more elegantly rounded form, without angulari- 
ties ; the skin thinner and more translucent ; the hair 
of the head is longer and finer, but other portions of the 
skin less coyered with hair; the nails smaller and thin- 
ner. 

The strength of the female is to that of the male as 
16 to 26. Her muscles contract with less energy, and 
are more easily wearied. The peculiarities of the con- 
struction of the bones of her pelvis and chest respective- 
ly give rise to peculiarities in the movements of the low- 
er and upper extremities ; hence the characteristic ban- 
ner of walking and movement of the arm in attempting 
to throw a stone. In the chapter on the voice we have 
already pointed out the female peculiarities in speaking 
and singing, and its more acute quality. 

With respect to her moral and intellectual peculiari- 
ties, these are manifested from the earliest infancy in 
the sports and games which she instinctively follows. 
Coming to maturity more rapidly than the male, she 
abandons these, though they may still be enjoyed by 
boys of her own age, whom, for the course of a year or 
two, she regards with neglect or even disrespect, a feel- 
ing soon after to be followed by timidity. Education 
and the position in which she may have been placed 
may, to a certain extent, control or disguise her habits, 
but they can never wholly obliterate the striking pre- 
dominance of her moral over her intellectual qualities, 
as compared with man. Essentially religious, her faith 
is applied to almost all the ordinary affairs of life, though 
when she finds that she has been deceived she is ever 
distrustful. From the earliest times it has been remark- 
ed that her revenge, more particularly when it concerns 
wounded pride, is implacable. Much more than the 

What is their relative strength? What are their relative moral 
and intellectual peculiarities ? 



OF SLEEP. 363 

male she is delighted with the adornments of dress. 
Her reasoning powers are less vigorous, though her sen- 
sations are more acute, yet she bears pain with more 
resignation than man. Her judgment is not so evenly 
balanced, and is often perverted by the preponderance 
of her feelings. 

The physiologist who is thus obliged to speak of the 
constitutional and mental imperfections of the female, 
may be permitted to turn with delight from the dry 
details of statistics and anatomy to the family and social 
relations, for it is therein that her beautiful qualities 
shine forth. At the close of a long life, checkered with 
pleasures and misfortunes, how often does the aged man 
with emotion confess that, though all the ephemeral ac- 
quaintances and attachments of his career have ended in 
disappointment and alienation, the wife of his youth is 
still his friend. In a world from which every thing else 
seems to be passing away, her affection alone is un- 
changed ; true to him in sickness as in health, in misfor- 
tune as in prosperity, true in the hour of death. 



CHAPTER XXV. 

OF SLEEP AND DEATH. 

Causes of the Necessity for Sleep. — Its Duration and 
Manner of Approach. — Manner of Awaking. — 
Cause of Xight-sleep. — Increased "Warmth required. 
— Connection of Sleep and Food. 

Of Dreams : their Origin and Phenomena. 

Of Death. — Old Age. — Internal Causes of Decline. — 
D aJbh by Accident and by Old Age. — TJie Hippo- 
I ' ■■ . — Fined Insensibility. 

OF SLEEP. 

One third of the life of man is spent in sleep, a condi- 
tion of modified sensibility, in which the mind performs 
its functions in an imperfect way, and voluntary motion 
is nearly su-pended. This state, occupying so large a 
portion of the short period of time allotted to us, is 
therefore well deserving of the consideration of the 
What portion of life is spent in sleep? 



364 NECESSITY OF SLEEP. 

physiologist, and the more so since it presents, in the 
various phenomena of dreams, significant illustrations 
of the manner of action of the nervous system. 

All animals sleep. Many, perhaps most, dream. The 
necessity for a season of repose arises from the prepon- 
derance of the waste of the system over its repair dur- 
ing our waking hours. By bringing the animal func- 
tions into a condition of rest, an opportunity is afforded 
for renovation, and the equilibrium can be maintained. 

In early infancy, when it is necessary for the nutritive 
operations to be carried forward with the utmost vigor, 
and attended with as little waste as possible, the whole 
time is spent in sleeping and eating. The waking peri- 
od is gradually increased as the child advances, but not 
so as to make it continuous, for the day is broken into 
intervals of sleep. Even at three or four years of age 
we sleep more than once a day. In mature life eight 
hours are on an average required, but the precise time 
varies with different individuals, and even with the same 
individual in different constitutional states. The time is 
not, however, always a true measure of the amount of 
rest, for sleep varies very much in the degree of its com- 
pleteness or intensity ; there is a slumber so disturbed 
that we are unrefreshed by it, and a sleep so profound 
that we awake weary. Old age, as it advances, admon- 
ishes us to spare the system as much as we may, for re- 
pair is conducted with difficulty ; and this period, char- 
acterized by its resemblance in so many respects to child- 
hood, like it, is often marked by frequently-recurring and 
prolonged slumber. Moreover, various accidental and 
other circumstances are liable at all times to disturb its 
proper periodicity — a warm afternoon, a hearty dinner, 
an ill-ventilated apartment, monotonous sounds, the at- 
tention devoted to one object, bodily quiescence, ceas- 
ing to think, the use of narcotics, extreme cold, a hori- 
zontal position, etc. 

Sleep is commonly preceded by a sense of drowsiness 
of more or less intensity, gradually followed by a loss 
of sensibility. Objects cease to make an impression on 
the eyes, the lids become heavy and close. If we are 

What are the causes for the necessity of sleep ? Is there any fixed 
period for the duration of sleep ? What is the order in which the 
senses are affected? 



HANNEB OF AWAKENING. 3G5 . 

not in the horizontal position, but require muscular sup- 
port, as in sitting, the head droops, and the hands seek 
a support. Successively the senses of smelling, hearing, 
and touch pass away, as the sight has done ; but, be- 
fore this progress is completed, we start at an} 1 - sound 
or disturbance, voluntary muscular action being instant- 
ly assumed, though in the midst of a surprise. We are 
nodding. If we are in the horizontal position, as in bed, 
the body is thrown into a form requiring the least mus- 
cular exertion — the limbs are semiflexed. As sight, 
smell, hearing, touch, again in succession fail, all volun- 
tary motions cease, those now executed being of a pure- 
ly automatic kind. The 'eyes are turned upward and in- 
ward, the iris is contracted, the heart and the lungs act 
more slowly but more powerfully ; a gentle delirium, 
which exists while the centres of the special senses are 
coming into repose, introduces us to profound and un- 
conscious sleep. 

This condition of profound sleep, though it may be 
quickly, is yet gradually reached by passing through 
certain well-marked stages. Once gained, we sleep with 
heaviness in the early part of the night, and more and 
more lightly as morning approaches. It would, how- 
ever, be erroneous to suppose that this falling into insen- 
sibility and awakening are perfectly continuous events; 
there are, undoubtedly, subordinate periods of more and 
less complete repose, but under no circumstances are we 
ever aware that we are asleep. 

At any time of the night sleep may be abruptly bro- 
ken, the mind resuming its power after passing through 
a momentary interval of confusion. Toward the close 
of the customary time, the senses resume their power in 
an order inverse to that in which they lost it — the 
touch, the hearing, the smell, the sight. For a short 
period after awakening, the organs seem to be in a state 
of unusual acuten ess, more particularly that of sight — 
an effect arising from the obliteration of the vestiges of 
old im] . From profound sleep we pass to the 

Waking state through an intermediate condition of 
slumber. In the former, the movements we may exe- 
cute, under the influence of external impressions, are 
wholly of an automatic kind, such as turning in bed in 

;at is the order in which the senses are restored on awakening? 



* 366 NIGHT-SLEEP. 

various positions. The length of time spent in sleep 
and slumber respectively is by no means constant, many 
causes increasing the one at the expense of the other. 
On awakening, we are apt to indulge in certain muscu- 
lar movements — we rub our eyes, stretch, and yawn. 
If we are suddenly aroused, our motions are feeble and 
uncertain on attempting to walk at once ; but if we 
spontaneously awake at an unusual period, and more 
particularly if it be toward morning, we commonly re- 
mark a clearness of intellect or mental power. Many 
of our most judicious and correct conclusions occur to 
us under these circumstances. 

Though it is said that the sleep of man lasts about 
eight hours, there are many variations. Authentic cases 
are on record in which individuals have, for a considera- 
ble time and apparently without injury, slept only for 
one hour, and others in which that state has been pro- 
longed for an entire week. Man shows much greater 
differences than other animals ; birds, for instance, sleep 
lightly, and cold-blooded animals generally profoundly. 
Since the object of sleep is to afford an opportunity for 
repairing the waste of the system, the length of the 
needful time depends on conditions that are themselves 
variable : the extent of the antecedent waste, and the ra- 
pidity of the repair. In winter we sleep longer and usu- 
ally deeper than in summer, for the hourly waste in win- 
ter is greater. Habit, however, controls us very much. 

It has been supposed by some that it is to habit that 
our tendency to sleep at night is to be imputed. It is, 
however, more properly to be attributed to the ordina- 
ry circumstances of our life — the day being spent in mus- 
cular or mental exercise, since we can then see to per- 
form our duties, and this tax upon the system being 
necessarily followed by a feeling of weariness. Those 
animals which seek their food in the dark sleep by day. 
It is not, therefore, to any external physical condition 
that we should impute, our nocturnal sleep, but to the 
interior condition of our system, though it is quite true 
that physical agents, such as cold, and others that have 
been mentioned, will provoke a sensation of drowsiness. 

Is there any constant period for slumber and sleep respectively? 
What are maxima and minima durations of sleep ? What is its ob- 
ject ? What is the cause of nocturnal sleep ? 



OF SLEEP. 367 

In sleep we require additional warmth, and this \vc 
obtain by instinctively using more clothing for the pur- 
se of economizing the animal heat. The amount of 
caloric generated in the system is diminished through 
the cessation of muscular exercise, and therefore reduc- 
tion of decay. The same may be said, to a certain ex- 
tent, of the waste of the brain through its intellectual 
acts, and of the nervous system generally. This dimin- 
ished amount of interstitial death corresponds to a di- 
minished respiration, the hourly amount of oxygen con- 
sumed exhibiting a decline. The negro, who is much 
more sensitive than the white man to this decline of tem- 
perature, instinctively envelops his head with clothing, 
so that the air may be warmed by its contact therewith 
before it enters the respiratory organs. For the same 
reason, he sleeps with his head toward the fire, while the 
white man sleeps with his away. On similar principles 
we may account for the control which food has over 
sleep, the one seeming, to a certain degree, to replace 
the other. The French proverb says, u He who sleeps, 
dines, n and this is true ; for during sleep the waste of 
the system is reduced to a minimum, and the necessity 
for food correspondingly diminished. The quality of 
the food likewise exerts an influence on the length of 
sleep, for that which is of a nutritious kind, and easily 
assimilated, can more speedily execute whatever repairs 
the system may demand. It is probably owing to his 
variable diet that, even in a state of perfect health, man 
Lb BO variable a sleeper, and that animals, the nature of 
whose food is so constant, sleep with so much uniform- 

Afl the necessary repairs are accomplished, we pass 
through a condition of slumber, and our organs gradu- 
ally awake in the manner that has been described. It 
is daring this intermediate | . thai is, toward the 

morning chiefly, as the brain is resuming its functions, 
that dreams occur. They may, however, happen at any 
other period of the night, though then they are liable to 
present greater incongruities and more obvious viola- 
tions of the proper oral ats. It is <juite con 

Wh j If increased warmth required? What din .re re- 

marked between the deeping of the white man and the negro? In 

a hat manner do dreams a. 



368 OF DREAMS. 

that morning dreams are more likely to be prophetic, for 
they are more likely to be in themselves true. 

Dreams never strike us with surprise, no matter what 
may be the extraordinary scenery they present — no mat- 
ter how great the violations of truth and reality. The 
dead may 'appear with the most astonishing clearness; 
their voices, perhaps long forgotten, may be heard ; we 
may be transported to places where we have spent past 
years of our lives; combinations of the most grotesque 
and impossible kinds may be spread before us : we ac- 
cept all as reality, perhaps not even suspecting that we 
dream. The germs from which have originated all these 
strange combinations are impressions stored up in the 
registering ganglia of the brain, more particularly in its 
optic thalami. These, as outward impressions have for 
the time ceased, are enabled to attract the attention of 
the mind, and emerge from their latent state. That all 
dreams originate in such impressions is illustrated by 
the history of the blind, who still dream of things that 
they formerly saw. 

One of the most extraordinary phenomena presented 
in the dreaming state is the instantaneous manner in 
which a long series of events may be offered to the 
mind, the exciting cause being truly of only a moment- 
ary duration. Some sudden noise arouses us, and, in 
the act of waking, a long drama connected with that 
noise appears before us ; or, in like manner, we are dis- 
turbed perhaps by a flash of lightning, and with that 
flash occurs a dream which seems to us to occupy a 
space of hours or even days, so many are the incidents 
with which it is filled. It has long been known that a 
like peculiarity has offered itself to those who have 
suffered by drowning, and have been subsequently re- 
stored. They have related that in their moment of su- 
preme agony, the whole series of events of their past 
life has, as it were, flowed in an instant upon them with 
the most appalling vividness, their good and evil works, 
and even the most trifling incidents presenting them- 
selves with distinctness — a tide of memory. 

From what source are these suggestions derived ? What is meant 
by the instantaneous presentment of events ? 



DEATH BY ACCIDENT OR OLD AGE. 369 



OF DEATH. 

At all periods of life, the functional activity of the 
system occasions a waste of its tissues by the interstitial 
death of their parts, and therefore involves a necessity 
of repair. So long as the reparation balances the waste, 
a healthy equilibrium is maintained; but when the nu- 
tritive powers decline, as old age approaches, a gradual 
deterioration of the system ensues. 

The period of greatest activity is also that of greatest 
waste, and of the most active and perfect repair, inter- 
stitial death and the removal of decayed material then 
occurring in the most rapid manner. The energy of 
life is thus dependent on the amount and completeness 
of death. 

At a later period, with advancing years, although the 
loss of substance through functional activity may be 
lessened, the renewal and restoration of the portions 
which are necessarily consumed are far more than cor- 
respondingly diminished. We thus become incapacita- 
ted corporeally and mentally, and, if no accident inter- 
venes, we die through mere old age. 

The death of individuals may therefore occur in two 
ways, by accident or by old age. But death from old 
age is very unusual, for even in the case of those who 
are very far advanced in life, its close is ordinarily 
brought about by some lesion or derangement of the 
vital organs, thus, in reality, constituting accidental 
death. 

Most men desire that their final scene maybe attend- 
ed with as little derangement as possible of their ordi- 
nary mental powers, and that it may be very brief. If 
this constitute the euthanasia, or happy death, it cer- 
tainly can not be thought that extreme old age is desir- 
able, constituting, as it does, along-continued and dreary 
The senses fail us in the same manner and in 
the same order that they do when we are falling asleep, 
their gradual deterioration bringing us back to the 
bel] - and imbecility of infancy. In the long in- 

terval daring which this is going on, the Bged man is not 

is it that deterioration of the system inevitably oeenrs? How 
is it that eventually death necessarily takes place? Why is it that 
death from old age is so unusual ? 

Q2 



370 GRADUAL DEATH. 4 

only a burden to himself, but a sad spectacle to every one 
around him ; his perceptions are being gradually blunt- 
ed ; and though he is, as it were, by degrees passing into 
a final slumber, it is in that disturbed way which all have 
witnessed when they fall asleep after severe fatigue. 

The different portions of the body die in succession : 
the system of animal life before that of organic, and of 
the former the sensory functions fail first, voluntary mo- 
tion next, while the power of muscular contraction un- 
der external stimulus still feebly continues. The blood, 
in gradual death, first ceases to reach the extremities, its 
pulsations becoming less and less energetic, so that, fail- 
ing to gain the periphery, it passes but a little way from 
the heart ; the feet and hands become cold as the circu- 
lating fluid leaves them, the decline of temperature grad- 
ually invading the interior. No one has ever yet of- 
fered a more accurate picture of the appearence of the 
dying than that presented by Hippocrates : " If the pa- 
tient lies on his back, his arms stretched out, and his 
legs hanging down, it is a sign of great weakness ; when 
he slides down in the bed it denotes death. If, in a 
burning fever, he is continually feeling about with his 
hands and fingers, and moves them up before his face 
and eyes as if he were going to take away something 
before them, or on his bed-covering as if he was picking 
or searching for little straws, or taking away some 
speck, or drawing out little flocks of wool, all this is a 
sign that he is delirious, and that he will die. When 
his lips hang relaxed and cold, when he can not bear 
the light, when he sheds tears involuntarily, when, doz- 
ing, some part of the white of the eye is seen, unless he " 
usually sleeps in that manner, these signs prognosticate 
danger. When his eyes are sparkling, fierce, and fixed, 
he is delirious, or soon will be so ; when they are dead- 
ened, as it were, with a mist spread over them, or their 
brightness lost, it presages death or great weakness. 
When the patient has his nose sharp, his eyes sunk, his 
temples hollow, his ears cold and contracted, the skin of 
his forehead tense and dry, and the color of his face 
tending to a pale green or leaden tint, one may give out 
for certain that death is very near, unless the strength 

In what order do the different parts of the body die ? Describe 
the Hippocratic face. 



THE AGONY. 371 

of the patient has been exhausted all at once by long 
watch ings, or by a looseness, or being a long time with- 
out eating/' 

Physiologists often quote the sentiment of Montaigne, 
"With how little anxiety do we lose the consciousness 
of light and of ourselves." By this they would convey 
the idea that the act of dying is as painless as the act 
of tailing asleep, and also as little perceived. They re- 
call the fact which seems to support this view, that 
those who have been recovered after apparent death 
from drowning, and after sensation has been totally lost, 
report that they have experienced no pain ; and, indeed, 
when we reflect that the sensory powers are the first to 
decline, the eve and the ear, at an early period in the 
article of death, failing to discharge their duty, and the 
general sense of touch becoming rapidly more and more 
obtuse, we can scarcely put any other interpretation 
upon the final struggles constituting what is so signifi- 
cantly called the agony, than that they are purely auto- 
matic and therefore unfelt. Doubtless the mind, in this 
solemn moment, is sometimes occupied with an instant- 
aneous review of impressions long before made upon 
the brain, and which offer themselves with clearness 
and energy now that present circumstances are failing 
to excite its attention, through loss of sensorial power 
of the peripheral organs, this state of things having also 
been testified to by those who have been recovered from 
drowning. 

•Life closes at last in various ways. Some pass away 
as though they were really falling asleep ; others with a 
dee]) sigh or groan ; others with a gasp ; and some with 
a convulsive straggle. „ 

What reason is there to supjHixj that the final agony is automatic? 



INDEX. 



A. 

Aber- 

Absorption, 66; blood-vessel. ?3; skin, 

- 

: diurnal a: 
153; raren in digestion, 

- 
Air- 

".. 1-57. 
Aliment, combustible, 16T. 
Allantoic 352. 

. 174. 
Amni * 

Animals, hot and cold blooded, 153. 
Annual receipts and wastes, 3. 
Aqueous humor. 8 
Areolar tissue, 335. 

Army and Navy di 
Arteries, 121 : fan 

Attraction, capillo 
Awakening. 
Axis cylinder, 211. 



Bell, discoveries c :". 

Bird, digestive tract of. 44: heat of, 

:. 144. 
Blood, 91 ; coagulation of, 93 ; composi- 
- 
99. 
Blood- 
Blood circulation, 108, 114. 
Blood cti -ion of, 105. 

•• functions of. 
Blood, porta 

Bread, 21: making of, C 

Breakfast. 

Breath, fir?* 

- ue, 1<">4. 
Bronchial tubes. 

-coveries of, 230, 315, 
319. 
Brunner'a glands, 54. 
Butt 



Calorification 

Capillarv .v 



Capillaby vessels. 123. 
Carbonic aci ■:. 
Cardiac ganglia, 121. 
Carnivora and herbivor; . 
Carpenter on sensorium, _• 7. 

. >. _ _. 
Castle-buildir. _ 
Catamenia. :- 
Cells, anim. 

u circulation in. 111. 

simple and nucleated, 39ft 

u vegetable, 327. 
Cells of blood. i-5. 
CeUular tissue. 33 1 
Ceeebellum. 2-:5. 240. 
Cerebro-spinal fluid, 241. 
Cere: 

ferine, 221. 

Choroid coat. 

Chyle, 71 : composition of, 75. 
corpuscles. " 

I cells, 306. 

3,128; capillars 113. 
124: festal, S52: portal, 115. 
Coagulation of blood, 93 ; of lymph, 7 B . 
Cochle-. - 
Cochlear nerv 

rum. 195. 
Coteactixity. 314, 317. 
Cooling agen 

- \ . __~. __ 
Corpus luteur 
Cranial nerve - 
Crevice, passage of -water I 
Cms cerebri, 235 : cerebelli, 235. 
-da of blood, 99. 

D. 

Deafness of animal 
Death, 369. 
Derma. - 

t. 336. 
Diaphragm, motions <-f, 14^ # 

/ 
I an of gases, 135 : general facts of, 
141. 

tive appamt 

DISCS Of Wor ; 

I 

Drpaujjpg, 368. 

Drum of ear. 



374 



JNDEX. 



Ductless glands, 188. 
Ducts, 832. 
Dugong, 117. 

E. 

Ear, 262. 

Embkyo, 348, 350. 

Endosmosis, 87 ; force of, 89 ; of 

137. 
Enteric juice, 54. 
Epidermis, 204. 
Equilibrium, conditions of, 4. 

u of temperature, 172. 

Eustachian tube, 266. 
Excretion, 190. 
Exhalation, 208. 
Exosmosis, 87. 
Eye, accessory apparatus of, 293. 

44 nervous mechanism of, 2S7. 

44 structure of, 279. 
Eyebrows, 293. 

F. 

Fabricius ab Aquapendente, 109. 

Facial nerve, 250. 

Faeces, 65. 

Fat, 58 ; introduction of, 69. 

Feeling, 298. 

Female peculiarities, 362. 

Fermentation, 61. 

Ferments, 62. 

Fibres, muscular, 307. 

Fibein, 19, 75, 80. 

Fibro-cellular tissue, 331. 

Fibrous tissue, 334. 

Fishes, circulation in, 115. 

" digestion of, 32. 

w respiration of, 142. 
Flour, 21. 

Foetus, circulation of, 352. 
Food, 5 ; classification of, 16. 
Franklin, experiments of, 277. 

G. 

Ganglia, 225, 226. 
Gases of blood, 103. 
44 intestine, 64. 
Gastric digestion, 33, 39, 51. 

44 juice, 36. 
Gelatin, 16, 51. 
Generation, 329. 
Germ cell, 338. 
Germinal membrane, 344. 
Gland, 178 ; ductless, 188. 

44 sebaceous, 206. 

44 sudoriparous, 206. 
Globulin, 100. 

Glosso-pharyngeal nerve, 251. 
Graafian vesicle, 339. 

H. 

Hsematin, 99-106. 
Hall, discoveries of, 230. 
Hand, 296. 

Harvey on circulation, 109. 
Hearing, 262. 
Heart, 10S ; fibres of, 118. 
44 lymphatic, 81. 



Heart, operation of, 127. 

44 rudimentary, 116. 

44 sounds of, 119. 
Heat, 8 ; animal, 158 ; plant, 160. 

44 equilibrium of, 162. 
Height of man, 359. 
Hepatic vessels, 181. 
Hibernation, 10, 168. 
Histogenetic food, 16. 
Hydra, 38. 

Hydraulic action, 130. 
Hydrochloric acid, 38. 



Insalivation, 28. 
Insect digestion, 43. 

44 respiration, 141. 
Interstitial death, 4. 
Intestine, 52. 

44 digestive fluids of the, 53. 

J. 
Jacob, membrane of, 2S8. 

K. 

Kidney, 190. • 

44 action of, 171. 
Kiestine, 202. 



Lachrymal gland, 293. 

Lactation, 199. 

Lacteals, 66 ; movements in, 71. 

Lactic acid, 57. 

Larynx, 325. 

Lenses, properties of, 283. 

Light, perception of, 288. 

Liver, 1S3 ; secretion of, 186. 

44 sugar and fat, 184. 
Lungs, 145. 

Lymph, 7S; flow of, 81. 
Lymphatic glands, 79. 
Lymphatics, 77. 

M. 

Malpighian bodies, 192. 

41 circulation, 193. 

Mammary gland, 197. 
Man, growth of, 357. 
Matters received, 7. 
Meconium, 183, 257. 
Medulla oblongata, 232 ; function of, 233. 
Meibomian glands, 293. 
Membranes, 89, 140 ; selecting, 90. 
Mesenteric glands, 66, 75. 
Milk, 17, 21, 198. 
Mitchell on Diffusion, 136. 
Mitral valve, 119. 
Mortality, 361. 
Motion, animal, 305; muscular, 306. 

44 of stomach, 39. 
Motor and sensory roots, 228. 
Motor-oculi nerve, 249. 
Mucus, 179. 
Muscular fibre, 307. 

44 44 contraction of, 312,315. 

44 4t non-striated, 308. 



INDEX. 



375 



N. 
Neetzs, 210. 

M fibres of, 211. • 

u function of fibres of, 214. 

14 function of vesicles of, 21G. 

11 vesicles of, 213. 
Nervous system controls heat, 173. 

u matter, waste of, 220. 
Nitrogen, protoxide of, 107. 
Nose, 300. 

O. 
Ocelli, 2TB. 

Ocular spectra, 292. 
Odobs, perception of, 301. 
Olivary bodies, 236. 
Ostrich, stomach of, 45. 
Ovaries, 338. 
Ovum in ovary, 339. 

u in oviduct, 342. 

" segmentation of, 343. 

P. 

Pancreas, 53. 

Papillae, 297. 

Papillary body, 295. 

Parotid saliva, 29. 

Pathetici. 249. 

Pepsin, 36, 40. 

Peptones, 47. 

Perilymph, 272. 

Perspiration, 208. 

Fever's bodies. 55. 

Phosphorus, 221. 

Plants, relation of, to animals, 24. 

" heat of, 160. 
Plasma, 101. 

Pneumogastric nerve, 251, 253. 
Pons varolii, 234. 
Portal circulation, 115, 1S2. 
Pre-existence, sentiment of, 247. 
Prehension, 295. 
Primitive trace, 348. „ 
Protein, IS. 
Psvchical powers, 242. 
Puberty, 339. 
Pulse, 120. 

R. 
Rarefied air, effect of, 168. 
Reaumur on digestion, 41. 
Reflex action, 

ring ganglia, 218. 
Rkpbodot 

Reptile re spir ation, 144 
-. 134. 
" effects of, 154. 

u explanation of , 151. 

M meehanigm of. l4->. 

M . •■-■ of, 147. 

mucosum, 2 
Retina. 

is, 318. 
f. 223. 
Rnmford on clothing, 164 
Ruminant, stomach of, 40. 
Running, 321. 



Saliva, 29, 30. 
Salivary digestion, 32. 
Salt, 47. 

" of blood, 103. 

u of intestine, 64. 
Sap, 112. 

Sarcolemma, 307. 
Scalse of ear, 271. 
Schwann, white substance of, -20. 
Sebaceous glands, 206. 
Secretion, 175. 

u by kidneys, 195. 
Selecting power, 81. 
Semicircular canals, 272. 
Senses, 261. 

Sensitiveness, measure of, 297. 
Serous membrane, 178.- 
Sexes, 358. 
Shelter, 165. 

Sight, long and short, 285. 
Skin, 171, 204. 
Sleep, 363. 
Smell, 299. 

Soap-bubble diffusion, 137. 
Soemmering, spot of, 282. 
Song and speech, 323. 
Sounds, 263 ; interference of, 270. 
" quality of, 273. 
u rudimentary, 323. 
Speaking machines, 326. 
Spectral impressions, 224. 
Speech, 322, 
Spermatozoa, 338. 
Sperm-cell, 336. 
Spinal Coed, 227. 
Spiracle, 142. 
Spiral vessels, 332. 
Soleen, 18S. 
Standing, 319. 
Star-like blood-cells, 105. 
Starch, digestion of, 56. 
Starvation, 167. 
Stereoscope, 291. 
Still layer, 124. 
Stomach, anatomy of, 34. 
M digestion, 33. 
" follicles of, 37. 
Striated muscular fibre, 308. 
Sudoriparous glands, 31, 206. 
Sugar, digestion of, 57. 
« in blood, 103. 
" of milk, 19, 203. 
Sweat, 209. 
Sympathetic System, 255, 200. 

" " fibres of, 212. 

" " functions of, 257. 

T. 
Taste, 302. 
Teeth, 28, 358. 

Temperature of man, 9, 12, 158. 
Testis, 337. 

Thalamus opticus, 235. 
Thoracic duct, T.\. 
Thought, double trains of, 246. 
Thymus, 188. 



376 



INDEX. 



Thyroid, 188. 

Tickling, 298. 

Time, perception of, 248. 

Tissue, cellular, 330 ; muriform, 331. 

Tongue, 303. 

Touch, 295, 298. 

Tracheal tubes, 146. 

Tradescantia, 112. 

Transudation, 207. 

Tricuspid valve, 118. 



Urea, 6, 194. 
Urine, 193. 



U. 



V. 



Vascular Absorption, 84. 

" tissue, 332. 
Veins, 125. 

Ventricles, 118; force of, 120. 
Venturi, principle of, 72. 
Vernix caseosa, 357. 
Vesicles, nerve, 213. 



Villi, 67. 

Vision, 277. 

" erect, 291. 

" limit of, 2S6. 

" single, 290. 

" subjective, 292. 
Vocal cords, 266-324. 
Voice, 321. 
Volkmann on muscular contraction, 

222. 
Von Bar, law of, 353. 

W. 

Walking, 320. 
Warming of rooms, 166. 
Water, use of, 6, 10. 
Weight of man, 3. 
Willis, circle of, 241. 
Wine making, 59. 



Zona pellucida, 340. 



THE END. 



